Type species

Gymnagnostus gongros Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, from the upper Furongian–lower Tremadocian of Mexico, by original designation.

Remarks

In many agnostoid trilobites the dorsal furrows of the exoskeleton are secondarily effaced, resulting in several smooth or nearly smooth lineages that are difficult to differentiate (e.g., Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968; Ahlberg, Reference Ahlberg1988). Early Ordovician highly effaced agnostoids have been variously assigned to Litagnostus Rasetti, Reference Rasetti1944, Leiagnostus Jaekel, Reference Jaekel1909, and Gymnagnostus Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968 (Nielsen, Reference Nielsen1997). Based on the study of juvenile specimens and parietal morphology, Palmer (Reference Palmer1955) and Robison and Pantoja-Alor (Reference Robison and Pantoja-Alor1968) noted that Litagnostus represents a diplagnostid genus characterized by having indications of a long “pseudagnostid-type” pygidial axis, whereas Gymnagnostus bears a shorter, parallel-sided posteroaxis of “geragnostid” aspect (see also Shergold et al., Reference Shergold, Laurie and Sun1990; Fortey and Owens, Reference Fortey and Owens1991; Nielsen, Reference Nielsen1997). As stated by Ahlberg (Reference Ahlberg1988), Gymnagnostus is morphologically very close to Leiagnostus, but the cephalon of the former is distinguished by its well-defined cephalic border and its faintly outlined basal lobes.

Gymnagnostus kobayashii new species

Figure 5.1–5.7

Diagnosis

A Gymnagnostus species with a moderately developed cephalic border; vestiges of axial furrows on the pygidial anteroaxis; a variably defined axial pygidial node; a shallow, proportionately wide pygidial border furrow, which is represented by an abrupt change in exoskeletal slope; and a pygidial border lacking marginal spines.

Description

Cephalon convex, subcircular in outline, subequal in length and width; acrolobe highly effaced, with faint indications of a delicate axial node, which is situated approximately one-third cephalic length from posterior margin; basal lobes partially outlined, indistinct anteriorly; cephalic border narrow, slightly convex, narrowing slightly laterally; cephalic border furrow shallow and narrow. Largest observed cephalon 3.4 mm long (sag.).

Pygidium convex, semiovate in outline, approximately as wide as long; acrolobe highly effaced, slightly constricted, with vestiges of axial furrows on M1 lobe; axial node variably developed, situated approximately one-third pygidial length from anterior margin; pygidial border narrow, weakly convex, lacking marginal spines; border furrow shallow, proportionately wide, represented by an abrupt change in exoskeletal slope; anterolateral corners of pygidium nearly right-angled; articulating half-ring narrow (sag.), arched, separated from the acrolobe by a very narrow articulating furrow. Largest observed pygidium 4 mm long (sag.).

Etymology

In honor of Teiichi Kobayashi, who provided one of the first comprehensive discussions on the systematics of smooth agnostoids (Kobayashi, Reference Kobayashi1937).

Types

Holotype, pygidium, MLP 35144 (Fig. 5.3), length 3.2 mm, width 3.3 mm; paratypes, three cephala and eight pygidia (MLP 35035a, 35061, 35062a, 35189b, 35209, 35248a,b, 35256, 35318c, 35323b, 35324b).

Occurrence

Pantipampa and lower Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

The best known species of Gymnagnostus from South America is G. bolivianus (Hoek in Steinmann and Hoek, Reference Steinmann and Hoek1912); a taxon that was fully described from the upper Furongian (Parabolina frequens argentina Zone) of the Cordillera Oriental (e.g., Harrington and Leanza, Reference Harrington and Leanza1957, figs. 21.2a, b, 23; Tortello and Esteban, Reference Tortello and Esteban2003, fig. 4.K–N, P–S; Esteban and Tortello, Reference Esteban and Tortello2007, Fig. 9A). The cephalon of G. bolivianus is identical to that of Gymnagnostus kobayashii n. sp., but the pygidium of the latter is distinguished by its wider border furrow and its slightly constricted acrolobe. Similarly, Gymnagnostus kobayashii differs from Gymnagnostus mexicanus Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, from the uppermost Furongian of Mexico (Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, pl. 97, figs. 15, 16, 19–22) and western Newfoundland, Canada (Fortey in Fortey et al., Reference Fortey, Landing and Skevington1982, pl. 2, fig. 6; Pratt, Reference Pratt1988, fig. 6Q), by having a shallow, relatively wide pygidial border furrow.

Gymnagnostus perinflatus (Harrington and Leanza, Reference Harrington and Leanza1957) from the upper Furongian of the Famatina Range and western Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 21.3; Tortello and Esteban, Reference Tortello and Esteban1999, figs. 5.P–T; Esteban and Tortello, Reference Esteban and Tortello2007, fig. 9.F), as well as Leiagnostus aff. turgidulus Harrington and Leanza, Reference Harrington and Leanza1957 from the lower Tremadocian of South Wales (Owens et al., Reference Owens, Fortey, Cope, Rushton and Basset1982, pl. 1, figs. b–d, f), further differ from Gymnagnostus kobayashii mainly in having a very narrow cephalic border. The type species, G. gongros Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968 (pl. 97, figs. 24–33) from the upper Furongian–lower Tremadocian of Mexico, is easily distinguished by showing a conspicuous pygidial axial node, a narrow pygidial border furrow, and well-defined posterolateral spines.

Harrington and Leanza (Reference Harrington and Leanza1957, p. 239) cited two fragmentary specimens of Gymnagnostus associated with Kainella, Leptoplastides marianus and Hapalopleura clavata, from an indeterminate locality of the Iruya area. Although this material was originally assigned to Gymnagnostus bolivianus (=“Gallagnostus” bolivianus), a further revision may show that it is conspecific with G. kobayashii.

Order Ptychopariida Swinnerton, Reference Swinnerton1915

Suborder Ptychopariina Swinnerton, Reference Swinnerton1915

Family Shumardiidae Lake, Reference Lake1907

Genus Conophrys Callaway, Reference Callaway1877

Type species

Conophrys salopiensis Callaway, Reference Callaway1877, from the upper Tremadocian of England, Wales and Nova Scotia, Canada, by subsequent monotypy.

Remarks

Fortey and Owens (Reference Fortey and Owens1987) regarded the presence of small to moderate-sized anterolateral glabellar lobes, a macropleural thoracic segment, and a transversely oval pygidium with an extended axis, as diagnostic features of Conophrys Callaway, Reference Callaway1877. As stated by Fortey and Owens (Reference Fortey and Owens1987) and Waisfeld et al. (Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001), the closely related taxon Shumardia Billings, Reference Billings1862 differs from Conophrys mainly in having larger, swollen anterolateral glabellar lobes, a subtriangular pygidium and a shorter pygidial axis, and in lacking macropleural spines and a well-defined pygidial rim. Although Conophrys was often regarded as a subgenus of Shumardia in the past, we follow Waisfeld et al. (Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001) and consider it at a generic level.

Conophrys sp. indet.

Figure 5.11, 5.12

Description

Cranidium semicircular in outline, gently convex (tr., sag.), sagittal length half posterior width, lacking surface sculpture; glabella little elevated above genal region, long, occupying ∽85% of the total cephalic length and one third of the posterior cephalic width; anterolateral glabellar lobes moderate-sized, not inflated nor extended back, protruding outward slightly beyond level of lateral margins of occipital ring, with their posterior edges behind midlength of the cranidium; preglabellar furrow weakly defined, very narrow and shallow, strongly pointed anteriorly; axial furrows parallel sided, relatively wide (tr.) and deep; occipital furrow faint, slightly convex forward medially; lateral furrows S1 and S2 incised proximally; occipital ring a little wider (tr.) than the rest of the glabella, slightly rounded posteriorly; fixed cheek wide (tr.), convex, semicircular in outline, merging with a rounded anterior cephalic margin; posterior margin transverse; posterior border furrow distinct, defining a narrow (exsag.) posterior border. Largest observed cranidium 1.2 mm long (sag.).

Pygidium subtrapezoidal, nearly twice as wide (tr.) as long (sag.), with a slightly forward curvature at posterior margin sagittally; axis somewhat tapered, rounded posteriorly, with four axial rings and a terminal piece, occupying ∽80% of the total pygidial length (excluding articulating half ring) and one third of the maximum pygidial width; articulating half ring crescentic, defined by a distinctive, forwardly curved articulating furrow; pleural fields gently convex, divided into five pleurae by deep, curved outward and backward interpleural furrows; border and border furrow indistinct; pygidial sculpture of coarse granules on both axial rings and pleural ribs. Available pygidium 0.9 mm long (sag.).

Materials

Nine cranidia and one pygidium (MLP 35035b, 35053a, 35059b,c, 35062b, 35068b,c, 35115, 35158b, 35283c) from the Pantipampa locality, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Conophrys sp. indet. belongs to a group of species of Conophrys that is characterized by having small anterolateral glabellar lobes. Within this group, Conophrys sp. indet. compares closely with those species that show a very faint preglabellar furrow, a smooth cranidium, and a sculpture of coarse granules on the pygidium.

Conophrys erquensis (Kobayashi, Reference Kobayashi1937) was originally described by Kobayashi (Reference Kobayashi1937, pl. 6, figs. 1–3) on the basis of scarce, poorly preserved specimens from the lower Tremadocian (“Kainella shales”) of southern Bolivia. Additionally, Harrington and Leanza (Reference Harrington and Leanza1957, fig. 24.2a, b) assigned to C. erquensis several cranidia and one pygidium from the lower Tremadocian of Tilcara (Fig. 1.1) which show high correspondence with Conophrys sp. indet. The cranidia described above (Fig. 5.11) share a glabellar outline, relative development of glabellar furrows, and proportions of the occipital ring with those of C. erquensis from Tilcara (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 24.2b), whereas the pygidium (Fig. 5.12) slightly differs in the relative length (sag.) of the axis (compare with Harrington and Leanza, Reference Harrington and Leanza1957, fig. 24.2a). Although this difference may lack crucial taxonomic significance, the specimens studied herein are left in open nomenclature pending the recovery of more pygidia and a comprehensive revision of the type material of C. erquensis.

Conophrys sp. indet. is distinguished from C. fabiani Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, from the lower Tremadocian of the Argentine Puna (Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, fig. 13.1–13.12), by having an anteriorly pointed glabella, a longer preglabellar area, and an ill-defined pygidial rim. Conophrys sp. indet. differs from Conophrys alata Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, from the upper Furongian–lower Tremadocian of Mexico (Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, pl. 99, figs. 13–18), because the former exhibits the posterior edges of the anterolateral glabellar lobes behind midlength of the cranidium, a longer and narrower pygidium, an indistinct pygidial rim, and a less indented posterior margin. The type species, C. salopiensis from the upper Tremadocian (C. salopiensis Biozone) of England, Wales and eastern Canada (e.g., Fortey and Owens, Reference Fortey and Owens1991, figs. 8m–r, 13a–j; Ebbestad, Reference Ebbestad1999, fig. 25.B), hardly differs from Conophrys sp. indet. except by showing slightly larger, better delineated anterolateral glabellar lobes.

Conophrys sulcatus Malanca, Reference Malanca1996, from the lower Tremadocian in the vicinity of the city of Salta, Cordillera Oriental (Malanca, Reference Malanca1996, pl. 1, figs. 1–12, pl. 2, figs. 1–14; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 29, fig. 17), also compares closely with Conophrys sp. indet.; however, the former is distinguished by its longer (sag.) glabella, its well-defined occipital furrow, and a little longer (sag.) postaxial region. Conophrys changshanensis Lu in Lu et al., Reference Lu, Chu, Chien, Zhou, Chen, Liu, Chen and Xu1976, from the lower Tremadocian of northwestern Hunan, China (Peng, Reference Peng1990b, pl. 5, fig. 7–11), differs mainly by having a deeper preglabellar furrow, and lacking granules on the pygidium. Conophrys rushtoni Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, from the lower Tremadocian of north Wales (Rushton, Reference Rushton1982, pl. 3, figs. 13–17, 19, 21; Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, p. 854–857) exhibits a more rounded and firmly impressed preglabellar furrow, a more transverse anterior margin of the cranidium, a transversely elongate pygidium, and a shorter pygidial axis.

Conophrys wrighti Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, from the lower Tremadocian of New Zealand (Wright et al., Reference Wright, Cooper and Simes1994, fig. 8.A–H; Waisfeld et al., Reference Waisfeld, Vaccari, Chatterton and Edgecombe2001, p. 857), differs from Conophrys sp. indet. mainly in having a sculpture of fine nodes on the cranidium. A group of species of Conophrys (e.g., C. pusilla [Sars, Reference Sars1835]; C. gaoluoensis Zhou in Zhou et al., Reference Zhou, Liu, Meng and Sun1977, illustrated by Peng, Reference Peng1990a; C. minutula [Harrington, Reference Harrington1938]) is characterized by having large, teardrop-shaped anterolateral glabellar lobes, and therefore it is easily distinguished from the material studied herein.

Suborder Olenina Burmeister, Reference Burmeister1843

Family Olenidae Burmeister, Reference Burmeister1843

Subfamily Pelturinae Hawle and Corda, Reference Hawle and Corda1847

Genus Leptoplastides Raw, Reference Raw1908

Type species

Conocoryphe salteri Callaway, Reference Callaway1877, from the upper Tremadocian of England, by original designation (Fortey and Owens, Reference Fortey and Owens1991).

Remarks

Henningsmoen (Reference Henningsmoen1957, p. 264) fully revised Leptoplastides Raw, Reference Raw1908, and regarded Parabolinopsis Hoek in Steinmann and Hoek, Reference Steinmann and Hoek1912 and Andesaspis Kobayashi, Reference Kobayashi1935 as junior synonyms. These concepts were followed by Robison and Pantoja-Alor (Reference Robison and Pantoja-Alor1968).

Leptoplastides marianus (Hoek in Steinmann and Hoek, Reference Steinmann and Hoek1912 )

Figure 5.8–5.10, 5.13–5.22

1912 Parabolinopsis mariana Hoek in Reference Steinmann and HoekSteinmann and Hoek, p. 226, pl. 7, figs. 1–3.

1935 Andesaspis argentinensis Reference KobayashiKobayashi, p. 67, pl. 11, figs. 1, 2 (only).

1957 Parabolinopsis mariana; Reference Harrington and LeanzaHarrington and Leanza, figs. 30.1, 30.7, 30.9 (only).

1957 Leptoplastides marianus; Reference HenningsmoenHenningsmoen, p. 266.

2010 Leptoplastides marianus; Reference Tortello and AceñolazaTortello and Aceñolaza, p. 157–159, figs. 2.a–n, 3.a–e (see for further synonymy).

2013 Leptoplastides marianus; Reference Tortello, Zeballo and EstebanTortello, Zeballo and Esteban, figs. 6.1–6.11, 7.1–7.8.

Holotype

Complete specimen from the Tremadocian of Cuesta de Iscayachi, southern Bolivia (Kobayashi, Reference Kobayashi1937, pl. 4, fig. 15).

Diagnosis

A species of Leptoplastides with a glabella defined by moderately converging axial furrows and a straight or slightly curved preglabellar furrow; anterior cranidial border furrow represented by a backwardly directed row of tiny pits; preglabellar field short (sag.) but distinct, of similar length or slightly longer (sag.) than anterior border; palpebral lobes moderately developed, situated opposite anterior third of glabella; pygidium with a tapering axis, 2 pairs of faint pleural furrows, and entire posterior margin. Largest observed cranidium 9.5 mm long (sag.).

Materials

One fragmentary axial shield, 55 cranidia, 46 librigenae and 12 pygidia (MLP 4937, 4947, 34968a, 34969b, 34970b, 34971, 34973b, 34975, 34977b, 34979b, 34980b, 34981b, 34982, 34983, 34988, 34990, 34991, 34993, 34994, 34997–35000, 35004a, 35005–35007, 35008b, 35009–35015, 35017–35019, 35022–35024, 35026, 35028, 35029, 35030b, 35032, 35037, 35055b, 35057b, 35067, 35098, 35129, 35130b, 35133, 35141, 35142a, 35149, 35150b, 35153b, 35157b, 35162, 35184, 35185, 35188, 35202b, 35205, 35216, 35239, 35246, 35251, 35263, 35267, 35276, 35280, 35287, 35302, 35304, 35308, 35309, 35311, 35312b, 35318b, 35321b, 35323a, 35332, 35350, 35352, 35353c, 35355b) from the Pantipampa and lower Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella meridionalis and Kainella teiichii zones.

Remarks

Harrington and Leanza (Reference Harrington and Leanza1957) revised Leptoplastides marianus in detail and regarded it as “one of the most abundant species in the Argentinian and Bolivian Tremadocian” (Harrington and Leanza, Reference Harrington and Leanza1957, p. 91). Although they synonymized it with both “Andesaspis” argentinensis Kobayashi, Reference Kobayashi1935 from the lower Tremadocian of the Incamayo area, and “Protopeltura” granulosa Harrington, Reference Harrington1938 from the ?upper Tremadocian of Tilcara, Waisfeld and Vaccari (Reference Waisfeld and Vaccari2003) showed that the latter represents a valid species of Leptoplastides, which is distinguished from L. marianus mainly by its smaller, more forwardly situated palpebral lobes, and its shorter (sag.) preglabellar field. In addition, Leptoplastides granulosus seems to have delicate marginal spines on the pygidium (Harrington, Reference Harrington1938, pl. 8, figs. 13, 18, 21; Harrington and Leanza, Reference Harrington and Leanza1957, figs. 29, 30.4, 30.6, 30.8).

Leptoplastides marianus is reported from different facies at several localities of the Cordillera Oriental but in most cases the material collected consists only of cranidia and librigenae (e.g., Rao and Tortello, Reference Rao and Tortello1998; Tortello and Rao, Reference Tortello and Rao2000; Tortello and Aceñolaza, Reference Tortello and Aceñolaza2010; Tortello et al., Reference Tortello, Zeballo and Esteban2013). Fortunately, the collections studied herein include some pygidia, which exhibit a tapering axis with two or three rings and a terminal piece, two faint pleural ribs, and an entire margin (Fig. 5.21, 5.22).

Cranidia of L. marianus from the Iruya area show slight variations in the length (sag.) of the preglabellar field (Fig. 5.9, 5.16), the course of the preglabellar furrow (Fig. 5.10, 5.17), and the degree of expression of the lateral glabellar furrows (Fig. 5.13, 5.14); a specific variability that was also documented in material from the lower Tremadocian of Abra de Zenta, Quebrada de Moya, and Incamayo (Tortello et al., Reference Tortello, Zeballo and Esteban2013 and references therein). Although the palpebral lobes of the specimens from the Quebrada de Moya (Tortello et al., Reference Tortello, Zeballo and Esteban2013, figs. 6.1–6.8, 7.1–7.7) are a little larger than those of material from other localities, such a difference may lack specific significance.

Leptoplastides marianus differs from the type species L. salteri (Callaway, Reference Callaway1877), from the upper Tremadocian of England (Henningsmoen, Reference Henningsmoen1957, pl. 2, fig. 14; Fortey and Owens, Reference Fortey and Owens1991, figs. 8.c–j, 9), because the latter bears a slightly shorter (sag.) preglabellar field, more anteriorly located genal spines, and deeper pleural furrows on the pygidium.

Subfamily Oleninae Burmeister, Reference Burmeister1843

Genus Parabolinella Brøgger, Reference Brøgger1882

Type species

Parabolinella limitis Brøgger, Reference Brøgger1882, from the uppermost part of the Alum Shale Formation in the Oslo region, Norway (subsequently designated by Bassler, Reference Bassler1915).

Parabolinella sp. indet.

Figure 5.23–5.29

Materials

Twenty-eight cranidia (MLP 4934, 4953, 34972, 34976, 35142b, 35243, 35269, 35270, 35273, 35275, 35282, 35284, 35285, 35289, 35298, 35312a, 35313, 35361, 35362, 35368a,b, 35371–35375) from the Pantipampa and Rodeo Colorado localities, Iruya area, northwestern Argentina, Santa Rosita Formation, Tremadocian, Kainella teiichii and Bienvillia tetragonalis zones.

Remarks

Waisfeld and Vaccari (Reference Waisfeld and Vaccari2003) noted the need to revise the morphologic range of Parabolinella argentinensis Kobayashi, Reference Kobayashi1936, which has been widely reported from many lower and upper Tremadocian localities of northwestern Argentina, and provisionally restricted this species to specimens from the type locality (Purmamarca; lowest Tremadocian, Jujuyaspis keideli Zone) (Kobayashi, Reference Kobayashi1936, pl. 15, figs. 1–5; Harrington, Reference Harrington1938, pl. 7, figs. 1, 8; Harrington and Leanza, Reference Harrington and Leanza1957, fig. 38.3; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 32, figs. 9–13). Recently, Monti and Confalonieri (Reference Monti and Confalonieri2013) and Monti (Reference Monti2015, unpublished) conducted a cladistic analysis of Parabolinella and regarded material from the lower Tremadocian of Santa Victoria and Iruya, previously assigned to P. argentinensis by Harrington and Leanza (Reference Harrington and Leanza1957, figs. 37.1, 37.2, 37.5–37.7, 38.4–38.6), as a new species characterized mainly by having a long (sag.), inflated preglabellar field, and an angular anterior cranidial margin. Parabolinella specimens studied herein seem to be conspecific with that material. Further specimens were described by Tortello et al. (Reference Tortello, Zeballo and Esteban2013, figs. 7.9–7.11, 8.1–8.10) from the lower Tremadocian of the Quebrada de Moya locality.

Subfamily Triarthrinae Ulrich, Reference Ulrich1930

Genus Bienvillia Clark, Reference Clark1924

Type species

Dikelocephalus? corax Billings, Reference Billings1865, from a late Cambrian limestone boulder in the Levis Formation at Levis in Quebec, Canada, by original designation.

Remarks

The closely allied olenid genera Triarthrus Green, Reference Green1832, Bienvillia Clark, Reference Clark1924, and Porterfieldia Cooper, Reference Cooper1953 are distinguished by the arrangement of transverse cephalic furrows in front of the glabella (Ludvigsen and Tuffnell, Reference Ludvigsen and Tuffnell1983). Bienvillia is characterized by having a well-defined anterior cranidial furrow, which is separated from the preglabellar furrow by a discernible, inflated preglabellar field. The Bienvillia species of northwestern Argentina include B. tetragonalis (Harrington, Reference Harrington1938), B. rectifrons (Harrington, Reference Harrington1938) and B. parchaensis (Harrington and Leanza, Reference Harrington and Leanza1957) (e.g., Henningsmoen, Reference Henningsmoen1957; Fortey, Reference Fortey1974; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003).

Bienvillia tetragonalis (Harrington, Reference Harrington1938)

Figure 5.30, 5.31

1938 Parabolinella tetragonalis Reference HarringtonHarrington, p. 196, 197, pl. 7, figs. 3, 4.

1957 Triarthrus tetragonalis; Reference Harrington and LeanzaHarrington and Leanza, p. 113–115, figs. 42.2–42.4 (only).

1957 Bienvillia tetragonalis tetragonalis; Reference HenningsmoenHenningsmoen, p. 144.

2003 Bienvillia tetragonalis; Reference Waisfeld and VaccariWaisfeld and Vaccari, p. 329, pl. 31, figs. 18–20.

2005 Bienvillia tetragonalis; Reference Zeballo and TortelloZeballo and Tortello, p. 137, fig. 4.S–T.

Holotype

Cranidium from the Tremadocian of the Tilcara area, Cordillera Oriental, Argentina (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 42.2).

Description

Cranidium subtrapezoidal, weakly convex, with straight to forwardly curved anterior margin and slightly downsloping fixed cheeks; glabella large, subquadrate, slightly longer (sag.) than wide (tr.), poorly elevated above genal region, surrounded by subparallel axial furrows and a medially curved backward preglabellar furrow; lateral glabellar furrows S1 and S2 subequal in development, deep, oblique backward, disconnected medially and not reaching axial furrows; occipital furrow deep and narrow, straight medially and somewhat oblique forward laterally; preglabellar field flat or slightly convex, occupying ∽13%–17% of the total cephalic length; anterior cephalic border very short (sag.), slightly upturned, delimited by a narrow (sag.) border furrow; anterior facial suture subparallel; eye ridge faint but visible, short, oblique backward; palpebral area of the fixigena narrow (tr.); palpebral lobe approximately one-fourth length of cranidium, with its anterior edge just in front of lateral extremities of S2, surrounded by a very faint palpebral furrow; posterior fixigena with a shallow border furrow and a narrow (exsag.) posterior border. Largest observed cranidium 6.8 mm long (sag.).

Materials

Five cranidia (MLP 35360, 35369, 35370, 35398, 35399) from the upper part of the Rodeo Colorado section, Iruya area, northwestern Argentina, Santa Rosita Formation, Tremadocian, Bienvillia tetragonalis Zone.

Remarks

The cranidia examined are few but clearly represent a species of Bienvillia with a proportionately long (sag.) preglabellar field, a subparallel anterior facial suture, a moderately developed palpebral lobe, and a glabella that is slightly longer than wide. Therefore, this material is assigned to Bienvillia tetragonalis (Harrington, Reference Harrington1938), which is well known from the eponymous zone in both the type locality (Alfarcito, east of Tilcara; Harrington, Reference Harrington1938; Harrington and Leanza, Reference Harrington and Leanza1957; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003; Zeballo and Tortello, Reference Zeballo and Tortello2005) and El Perchel area (Waisfeld and Vaccari, Reference Waisfeld and Vaccari2008).

Bienvillia rectifrons (Harrington, Reference Harrington1938), from the upper Tremadocian of northwestern Argentina (Harrington, Reference Harrington1938, pl. 8, figs. 17, 19–21; Harrington and Leanza, Reference Harrington and Leanza1957, fig. 43.2a–g; Přibyl and Vanĕk, Reference Přibyl and Vanĕk1980, pl. 9, figs. 6, 7; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 31, figs. 15–17; Tortello and Esteban, Reference Tortello and Esteban2014, fig. 3.16–3.23, 3.25), differs from B. tetragonalis mainly in possessing a longer (sag.) preglabellar field. Bienvillia parchaensis (Harrington and Leanza, Reference Harrington and Leanza1957), from the upper Tremadocian of the Incamayo area, southern Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, figs. 43.1a–h, 44.1a–e; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 31, figs. 12–14), shows, in addition, larger (exsag.) palpebral lobes (Harrington and Leanza, Reference Harrington and Leanza1957; Ludvigsen and Tuffnell, Reference Ludvigsen and Tuffnell1983).

Order Asaphida Salter, Reference Salter1864 emend. Fortey and Chatterton, Reference Fortey and Chatterton1988

Superfamily Asaphoidea Burmeister, Reference Burmeister1843

Family Asaphidae Burmeister, Reference Burmeister1843

Subfamily Isotelinae Angelin, Reference Angelin1854

Genus Asaphellus Callaway, Reference Callaway1877

Type species

Asaphus homfrayi Salter, Reference Salter1866, from the Tremadocian of North Wales, by original designation.

Remarks

Meroi Arcerito et al. (Reference Meroi Arcerito, Waisfeld and Balseiro2015) discussed the morphological variability of Asaphellus and, based mainly on material from El Perchel area, described in detail several representative species from the Tremadocian of the Cordillera Oriental (e.g., A. stenorhachis [Harrington, Reference Harrington1938]; A. isabelae Meroi Arcerito, Waisfeld and Balseiro, Reference Meroi Arcerito, Waisfeld and Balseiro2015; Asaphellus sp. 1 sensu Meroi Arcerito, Waisfeld and Balseiro, Reference Meroi Arcerito, Waisfeld and Balseiro2015). As shown below, the Pantipampa and Rodeo Colorado sections include well-preserved specimens of these taxa.

Asaphellus catamarcensis Kobayashi, Reference Kobayashi1935

Figure 6.1–6.15

Figure 6 Asaphellus catamarcensis Kobayashi, Reference Kobayashi1935 from the Santa Rosita Formation in the Iruya area, northwestern Argentina: (1) cranidium, MLP 34985, ×1.7; (2) cranidium, MLP 34992, ×1.7; (3) librigena, MLP 35003, ×1.7; (4) hypostome, MLP 34980a, ×1.7; (5) hypostome, MLP 35025, ×1.7; (6) pygidium, latex cast, MLP 34970a, ×1.7; (7) librigena, MLP 34989, ×1.7; (8) pygidium, MLP 34979a, ×1.7; (9) pygidium, MLP 34973a, ×1.7; (10) pygidium, MLP 34996, ×1.7; (11) pygidium, MLP 34977a, ×1.7; (12) pygidium, MLP 34984, ×1.7; (13) pygidium, MLP 35031, ×1.7; (14) pygidium, MLP 35002, ×1.7; (15) pygidium, MLP 34986, ×1.7. All specimens from Pantipampa.

1935 Asaphellus? catamarcensis Reference KobayashiKobayashi, p. 65, 66, pl. 11, figs. 11–15.

1957 Asaphellus catamarcensis; Reference Harrington and LeanzaHarrington and Leanza, p. 147, fig. 65.7, 65.8 (only).

2000 Asaphellus catamarcensis; Reference Tortello and RaoTortello and Rao, p. 72, 73, fig. 3T–V.

2010 Asaphellus catamarcensis; Reference Tortello and AceñolazaTortello and Aceñolaza, p. 162, fig. 4.a–4.i (see for further synonymy).

2015 Asaphellus catamarcensis; Reference Meroi Arcerito, Waisfeld and BalseiroMeroi Arcerito, Waisfeld and Balseiro, fig. 6.A–D.

Lectotype

Pygidium from the lower Tremadocian of the Incamayo area, Cordillera Oriental, Argentina (Kobayashi, Reference Kobayashi1935, pl. 11, fig. 14; Meroi Arcerito et al., Reference Meroi Arcerito, Waisfeld and Balseiro2015, fig. 6A).

Description

Cranidium gently convex (sag., tr.), wider than long, with pointed anterior margin and moderately downsloping fixed cheeks; glabella very long, unfurrowed, weakly elevated above genal region, poorly defined by weak axial and preglabellar furrows, constricted between palpebral lobes, rounded anteriorly, reaching anterior border furrow; posterior half of the glabella much wider (tr.) than anterior half; glabellar length (sag.) represents ∽80%–84% of the total length of the cranidium; axial node absent; occipital ring not differentiated; socket for reception of first thoracic articulating half-ring very short (sag.), well defined by a delicate furrow; anterior cranidial border slightly convex, delimited by an anterior border furrow which is represented by a change in slope of exoskeleton; anterior facial suture diverging at an angle of 45º to the exsagittal line; palpebral area of the fixigena narrow (tr.); eyes small, situated adjacent to mid-length of cranidium; posterior facial suture oblique backward and outward, sinuous; posterior fixigena wide (tr.), with a shallow border furrow and a narrow (exsag.), convex posterior border; librigenae with wide and depressed border, which narrows backward; genal angles produced into long spines continuing curvature of lateral margin. Largest observed cranidium 27.5 mm long (sag.).

Hypostome subpentagonal in outline, as long (sag.) as wide (tr.); anterior lobe of median body large, slightly convex, ovate, as long as wide, with an incision sagitally close to its apex, occupying approximately two-thirds of the total length of the hypostome, tapering posteriorly to meet with a pair of maculae; posterior lobe short (sag.) and weakly convex, with its posterior margin slightly pointed backward; anterior wings subtriangular, broad; lateral border wide, depressed, of uniform width; posteromedian margin having an indentation.

Pygidium semielliptical in outline, much wider than long, somewhat convex; pygidial axis long and narrow, little elevated above level of pleural fields, delimited by variably developed axial furrows, ∽23%–26% of total width of pygidium at anterior extremity, tapering toward posterior at anterior half and nearly parallel sided at posterior half, with traces of segmentation on its anterior part, ending in a more or less inflated point which reaches posterior border furrow; length of axis ∽85% of that of pygidium on sagittal line; articulating half ring very narrow (sag.), delimited by a straight and shallow furrow; pleural field smooth, downsloping; anterior border narrow (exsag.) and convex, clearly delimited by a shallow furrow; lateral and posterior border furrow weak, represented by a change of slope of the exoskeleton; lateral and posterior border variably developed, weakly concave to flat; posterior margin can show a small indentation. Largest observed pygidium 22 mm long (sag.).

Materials

Two cranidia, seven librigenae, two hypostomes, and 17 pygidia (MLP 34970a, 34973a, 34974, 34977a, 34978, 34979a, 34980a, 34981a, 34984, 34985, 34986, 34987b, 34989, 34992, 34995, 34996, 35001–35003, 35004b, 35008a, 35020, 35025, 35027, 35031) from the middle part of the Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella meridionalis Zone and basal K. teiichii Zone.

Remarks

Kobayashi (Reference Kobayashi1935) briefly described Asaphellus catamarcensis on the basis of one fragmentary cranidium, one free cheek, one hypostome, and two pygidia from the Incamayo area. Subsequently Harrington and Leanza (Reference Harrington and Leanza1957) redescribed A. catamarcensis and reported it from numerous upper Furongian and lower and upper Tremadocian localities of the Cordillera Oriental, as well as from the uppermost Furongian of the Famatina System in the La Rioja Province. Because the morphologic range recognized by Harrington and Leanza (Reference Harrington and Leanza1957) is quite wide, Waisfeld and Vaccari (Reference Waisfeld and Vaccari2003) pointed out the need to critically revise the diagnosis and stratigraphic position of this species.

Because the original description was insufficient for a complete understanding of Asaphellus catamarcensis, Meroi Arcerito et al. (Reference Meroi Arcerito, Waisfeld and Balseiro2015, fig. 6) re-illustrated the type series and designated a pygidium as the lectotype. Such specimens exhibit small eyes, genal spines continuing curvature of lateral cephalic margin, a faint but perceptible pygidial axis, and a well-developed pygidial border. Among the numerous specimens assigned by Harrington and Leanza (Reference Harrington and Leanza1957) to A. catamarcensis, only the pygidia illustrated in their figs. 65.7 and 65.8 accord with the type material. In addition, specimens from Incamayo and Abra de Zenta were described by Tortello and Rao (Reference Tortello and Rao2000, fig. 3.T–3.V) and Tortello and Aceñolaza (Reference Tortello and Aceñolaza2010, fig. 4.a–4.i), respectively, in association with Leptoplastides marianus, Pseudokainella and Kainella meridionalis.

Furthermore, A. catamarcensis from the Iruya area is restricted to the lower part of the Pantipampa section (Fig. 2). As in material from Incamayo and Abra de Zenta, the pygidia studied herein show variations in the degree of expression of the axial furrows (Fig. 6.10, 6.12, 6.13), the width (tr.) of the border (compare Fig. 6.8, 6.11, 6.12), and the outline of the axis, which ends in a more or less inflated point (Fig. 6.9, 6.12). A similar variability is seen in the type series of A. catamarcensis (see Meroi Arcerito et al., Reference Meroi Arcerito, Waisfeld and Balseiro2015, fig. 6.A–C). Although Meroi Arcerito et al. (Reference Meroi Arcerito, Waisfeld and Balseiro2015) prefer to restrict A. catamarcensis to the type series from Incamayo (Kobayashi, Reference Kobayashi1935), we regard it as a taxon with a wider representation in the lower Tremadocian (Cordylodus angulatus Zone) of northwestern Argentina.

Asaphellus catamarcensis differs from A. jujuanus Harrington, Reference Harrington1938, from the upper Tremadocian of the Cordillera Oriental (e.g., Harrington and Leanza, Reference Harrington and Leanza1957, fig. 66.7, 66.12; Tortello and Esteban, Reference Tortello and Esteban2014, fig. 7.1–7.19), in having a more oblique posterior facial suture, longer genal spines, smooth pleural fields, and a less depressed pygidial border. It is distinguished from A. nazarenensis Tortello and Esteban, Reference Tortello and Esteban2014, from the upper Tremadocian of northwestern Argentina (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 8.1–8.6), in possessing a narrower (tr.) palpebral area of the fixigena and a more developed pygidial border; and from A. kayseri (Kobayashi, Reference Kobayashi1937) sensu Harrington and Leanza (Reference Harrington and Leanza1957, figs. 74, 75) (Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 22, figs. 7–9) by lacking pleural furrows on the pygidium and having smaller palpebral lobes and a wider pygidial border. Asaphellus catamarcensis further differs from partially effaced species of Asaphellus (e.g., A. inflatus Lu in Wang, Reference Wang1962; A. yanheensis Yin in Yin and Li, Reference Yin and Li1978; A. homfrayi [Salter, Reference Salter1866]; A. isabelae Meroi Arcerito, Waisfeld and Balseiro, Reference Meroi Arcerito, Waisfeld and Balseiro2015) in showing perceptible axial furrows on the pygidium.

Asaphellus clarksoni new species

Figure 7.1–7.15

Figure 7 Asaphellus clarksoni n. sp. from the Santa Rosita Formation in the Iruya area, northwestern Argentina: (1) librigena, latex cast, MLP 35224, ×2.2, Pantipampa (P); (2) cranidium, MLP 35327, ×1.8, Rodeo Colorado (RC); (3) cranidium, MLP 35325, ×2.2, RC; (4) librigena, MLP 35349a, ×2.2, RC; (5) librigena, MLP 35335, ×1.8, RC; (6) cranidium, MLP 35324a, ×2.2, RC; (7) pygidium, MLP 35199, ×2.5, P; (8) pygidium, MLP 35260, ×2.5, P; (9) pygidium, latex cast, MLP 35200, ×2.5, P; (10) pygidium, latex cast, MLP 35253, ×2.5, P; (11) pygidium, MLP 35244, ×2.2, P; (12) fragmentary pygidium, MLP 35279, ×2.2, P; (13) pygidium (holotype), MLP 35252, ×2.2, P; (14) pygidium, MLP 35206, ×2.2, P; (15) pygidium, MLP 35355a, ×2.2, RC.

Diagnosis

A species of Asaphellus with an effaced cranidium, a well-defined pygidial axis, faint but perceptible pleural furrows, and a distinct, concave pygidial border.

Description

Cranidium effaced, slightly convex (sag., tr.), wider than long, pointed anteriorly, with moderately downsloping fixed cheeks; glabella highly effaced; axial node weak, situated close to the posterior cranidial margin; socket for reception of first thoracic articulating half-ring very short (sag.), defined by a delicate furrow; anterior border furrow very shallow, delimiting a slightly upturned anterior border; anterior facial suture clearly diverging in front of eyes, meeting mesially in broad ogive; palpebral area of the fixigena narrow (tr.); palpebral lobe arcuate, situated at or slightly behind cranidial midpoint, occupying ∽15% of the total length (sag.) of the cranidium; posterior facial suture oblique backward and outward, sinuous; posterior fixigena with a very wide (exsag.) and shallow border furrow and a linear posterior border; librigenae showing a low eye socle, a wide and concave border, and a broad-based, short genal spine that continues curvature of lateral margin. Largest observed cranidium 23 mm long (sag.).

Pygidium semicircular in outline, scarcely convex, width approximately twice length; axis elevated above level of pleural fields, ∽25% of total width of pygidium at anterior extremity, slightly tapered at anterior half and nearly parallel sided at posterior part, with faint indications of seven rings and a bulbous terminal piece; length of axis ∽83%–85% of that of pygidium on sagittal line; articulating half ring extremely narrow (sag.), crescentic; pleural field only slightly downsloping, with two or three faint but perceptible wide shallow pleural furrows, among which the first is the most distinct; border furrow indicated by an abrupt change of slope of the exoskeleton; border well-developed, concave; border plus border furrow occupies ∽15%–17% of the total pygidial length; doublure broad, covered with 15–18 terrace ridges following the doublural contour. Largest observed pygidium 15.5 mm long (sag.).

Etymology

Dedicated to Dr Euan N. K. Clarkson (University of Edinburgh, Scotland).

Types

Holotype, pygidium, MLP 35252 (Fig. 7.13), length 10.5 mm, width 20 mm; paratypes, 7 cranidia, 12 librigenae, 1 thorax and 25 pygidia (MLP 35199, 35200, 35206, 35207, 35210, 35217–35224, 35235, 35238, 35241, 35242, 35244, 35245, 35253, 35257–35262, 35278, 35279, 35286, 35306, 35324a, 35325, 35327, 35335, 35336, 35338, 35344, 35348, 35349a, 35351, 35355a).

Occurrence

Upper Pantipampa and lower Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Harrington and Leanza (Reference Harrington and Leanza1957) assigned several specimens to A. catamarcensis whose affinity needs to be revised. A complete exoskeleton from the lower Tremadocian of the Santa Victoria area shows an effaced cranidium, traces of pygidial pleural furrows and a distinct pygidial border (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 64.3), and therefore it may be conspecific with A. clarksoni n. sp. Similarly, some pygidia of Asaphellus sp. from the El Perchel area (Meroi Arcerito et al., Reference Meroi Arcerito, Waisfeld and Balseiro2015, fig. 7.B, C, E) exhibit a well-developed border and vestiges of pleural furrows which resemble those of A. clarksoni.

Beds with A. clarksoni lie above those containing A. catamarcensis (Fig. 2). The latter species is particularly similar to A. clarksoni, but differs in having a better defined anterior cranidial border furrow and pleural fields without furrows. The new species from Iruya also shows similarities with Asaphellus jujuanus Harrington, Reference Harrington1938, from the upper Tremadocian of the Cordillera Oriental (e.g., Harrington and Leanza, Reference Harrington and Leanza1957, fig. 66.7, 66.12; Tortello and Esteban, Reference Tortello and Esteban2014, fig. 7.1–7.19), which possesses a pygidium with faint indications of pleural furrows and a broad border. Asaphellus clarksoni differs by having an indistinct glabella, smaller palpebral lobes, a more oblique posterior facial suture, and fewer rings on the pygidial axis.

Asaphellus clarksoni is distinguished from A. kayseri (Kobayashi, Reference Kobayashi1937), from the Tremadocian of northwestern Argentina (Harrington and Leanza, Reference Harrington and Leanza1957, figs. 74, 75; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 22, figs. 7–9), by having a less defined glabella, a more developed pygidial border, and fewer axial rings on the pygidium. It differs from Asaphellus nazarenensis Tortello and Esteban, Reference Tortello and Esteban2014, from the upper Tremadocian of the Nazareno area, Cordillera Oriental (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 8.1–8.6), because the latter shows a perceptible glabella, pleural fields lacking furrows, and a narrower pygidial border.

The type species, Asaphellus homfrayi (Salter, Reference Salter1866) from the upper Tremadocian of Great Britain (e.g., Fortey and Owens, Reference Fortey and Owens1991, figs. 3.l–u, 7.a–g, 8.a, b), differs from A. clarksoni mainly by its pleural fields without furrows. Asaphellus graffi (Thoral, Reference Thoral1946), from the Floian of southern France (Courtessole et al., Reference Courtessole, Pillet, Vizcaïno and Eschard1985, pl. 11, figs. 1–4), exhibits a better delineated glabella and a shorter (sag.), uniformly tapered pygidial axis. Asaphellus cf. graffi, from the upper Tremadocian of Wales (Fortey and Owens, Reference Fortey and Owens1992, fig. 4a–g), is similar in most of the essential features to A. clarksoni, although the former has a more concave frontal area. Asaphellus stenorhachis (Harrington, Reference Harrington1938) is easily distinguished by showing a highly effaced pygidum (see below).

Asaphellus stenorhachis (Harrington, Reference Harrington1938)

Figure 8.1–8.17

Figure 8 Asaphids from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–17) Asaphellus stenorhachis (Harrington, Reference Harrington1938): (1) cranidium, MLP 35396, ×2.2, Rodeo Colorado (RC); (2) pygidium, MLP 35383, ×3, RC; (3) cranidium, MLP 35367, ×2.2, RC; (4) fragmentary cranidium, MLP 35385, ×2.2, RC; (5) cranidium, MLP 35384, ×1.4, RC; (6) librigena, MLP 35316, ×2.2, RC; (7) cranidium, MLP 35381a, ×2.2, RC; (8) cranidium, MLP 35381b, ×2.2, RC; (9) pygidium, MLP 35314, ×2.2, RC; (10) pygidium, MLP 35364, ×2.2, RC; (11) pygidium, MLP 35211, ×2.2, Pantipampa (P); (12) pygidium, MLP 35382, ×2.2, RC; (13) pygidium, MLP 35272a, ×2.2, P; (14) pygidium, MLP 35386, ×2.2, RC; (15) pygidium, MLP 35381c, ×2.2, RC; (16) pygidium, MLP 35358, ×2.2, RC; (17) pygidium, MLP 35376, ×1.6, RC. (18–20) Asaphellus isabelae Meroi Arcerito, Waisfeld and Balseiro, Reference Meroi Arcerito, Waisfeld and Balseiro2015: (18) pygidium, MLP 35291, ×2, P; (19) pygidium, MLP 35303, ×2, P; (20) pygidium, MLP 35290, ×2, P.

1938 Illaenus stenorhachis Reference HarringtonHarrington, p. 182, 183, pl. 5, fig. 18.

1957 Asaphellus jujuanus Reference Harrington and LeanzaHarrington and Leanza, fig. 66.6, 66.8, 66.9 (only).

2015 Asaphellus stenorhachis; Reference Meroi Arcerito, Waisfeld and BalseiroMeroi Arcerito, Waisfeld and Balseiro, p. 141–144, figs. 8.A–M, 9.A (see for further synonymy).

Holotype

Fragmentary thorax and pygidium from the Tremadocian of the Tilcara area, Cordillera Oriental, Argentina (Harrington, Reference Harrington1938, pl. 5, fig. 18; Harrington and Leanza, Reference Harrington and Leanza1957, fig. 93.3).

Materials

Ten cranidia, eight librigenae and twenty-six pygidia (MLP 35211–35215, 35272a, 35305, 35314–35316, 35358, 35359, 35363–35367, 35376–35380, 35381a–e, 35382–35386, 35388–35397) from the upper Pantipampa and Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, Tremadocian, Kainella teiichii and Bienvillia tetragonalis zones.

Remarks

The material studied shows undefined cephalic axial furrows; a slightly divergent anterior facial suture; arcuate, distinct palpebral lobes; and extremely faint pygidial axial furrows. Thus, it is assigned to Asaphellus stenorhachis (Harrington, Reference Harrington1938); a highly effaced asaphid that has been fully revised by Meroi Arcerito et al. (Reference Meroi Arcerito, Waisfeld and Balseiro2015).

Asaphellus stenorhachis compares most closely with partially effaced species of Asaphellus (see a complete discussion in Meroi Arcerito et al., Reference Meroi Arcerito, Waisfeld and Balseiro2015). It strongly resembles Asaphellus sp., from the Tremadocian of the Nazareno area, Cordillera Oriental (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 8.8–8.12), in sharing an effaced, semicircular pygidium with a moderately developed border and very faint indications of a long tapering axis; however, the cranidium of A. stenorhachis seems to differ from that of Asaphellus sp. by its proportionately larger palpebral lobes.

Two cranidia from the Bienvillia tetragonalis Zone of Río Iturbe (Cordillera Oriental), originally referred to as Asaphellus jujuanus by Harrington and Leanza (Reference Harrington and Leanza1957, fig. 66.6, 66.9), exhibit a fully effaced glabella and anterior border furrow, and an oblique posterior facial suture; therefore, they are reassigned herein to A. stenorhachis. In addition, an associated librigena showing a distinct eye socle and a small genal spine (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 66.8) is considered conspecific.

Asaphellus isabelae Meroi Arcerito, Waisfeld and Balseiro, Reference Meroi Arcerito, Waisfeld and Balseiro2015

Figure 8.18–8.20

2015 Asaphellus isabelae Reference Meroi Arcerito, Waisfeld and BalseiroMeroi Arcerito, Waisfeld and Balseiro, p. 144, figs. 7G, 9B, 10A–M.

Holotype

Cranidium from the Tremadocian of Quebrada del Arenal, El Perchel area, Cordillera Oriental, Argentina (Meroi Arcerito et al., Reference Meroi Arcerito, Waisfeld and Balseiro2015, fig. 10E).

Materials

Eight pygidia and a few fragmentary, delicate cranidia (MLP 35283b, 35288, 35290, 35291, 35301, 35303, 35320, 35357) from the uppermost Pantipampa section and the lower Rodeo Colorado section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

A few asaphid specimens collected from the Iruya area have a proportionately large size (largest available pygidium 25 mm long), a semicircular outline, a very low and uniform convexity, and completely obliterated furrows, showing a degree of effacement that is higher than that of Asaphellus stenorhachis. This material accords with Asaphellus isabelae; a delicate, smooth asaphid recently described in great detail by Meroi Arcerito et al. (Reference Meroi Arcerito, Waisfeld and Balseiro2015, figs. 7G, 8.B, 10.A–M) from the Kainella meridionalis and K. teiichii zones of El Perchel, Cordillera Oriental.

Subfamily Ogygiocarinidae Raymond, Reference Raymond1937

Genus Ogygiocaris Angelin, Reference Angelin1854

Type species

Trilobus dilatatus Brünnich, Reference Brünnich1781, from the Middle Ordovician of Baltica, by original designation.

Remarks

Harrington and Leanza (Reference Harrington and Leanza1957), Henningsmoen (Reference Henningsmoen1960), Fortey and Owens (Reference Fortey and Owens1978), Waisfeld and Vaccari (Reference Waisfeld and Vaccari2006) and Hansen (Reference Hansen2009) discussed in detail the diagnostic features of Ogygiocaris. Waisfeld and Vaccari (Reference Waisfeld and Vaccari2006) regarded both Ogygiocarella Harrington and Leanza, Reference Harrington and Leanza1957 and Araiorhachis Přibyl and Vanĕk, Reference Přibyl and Vanĕk1980 as junior synonyms of Ogygiocaris, which is followed here.

Ogygiocaris? iruyensis new species

Figure 9.1–9.8

Figure 9 Ogygiocaris? iruyensis n. sp. and Niobe (Niobella) inflecta (Harrington and Leanza, Reference Harrington and Leanza1957) from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–8) Ogygiocaris? iruyensis n. sp.: (1) cranidium, MLP 35163, ×2.6; (2) pygidium, MLP 35161, ×3; (3) pygidium (holotype) MLP 35158a, ×3; (4) pygidium, MLP 35160, ×3; (5) pygidium, latex cast, MLP 35159, ×3; (6) pygidium, MLP 35053b, ×3; (7) pygidium, MLP 35154, ×3; (8) pygidium, MLP 35043a, ×2.3. (9–13) Niobe (Niobella) inflecta (Harrington and Leanza, Reference Harrington and Leanza1957): (9) cranidium, MLP 35054, ×1.3; (10) cranidium, MLP 35050b, ×1.3; (11) pygidium, latex cast, MLP 35089b, ×1.3; (12) pygidium, latex cast, MLP 35109, ×1.3; (13) pygidium, MLP 35094, ×1.3. All specimens from Pantipampa.

Diagnosis

A species of Ogygiocaris? with an anteriorly pointed glabella; pygidial axis with marked anterior five rings and extremely faint or indistinct posterior four rings, ending in blunt point; pleural fields crossed by five oblique furrows, which are shallow, straight to slightly curved, and end at level of doublural margin; anterior part of the doublural margin slightly undulating; paradoublural line indistinguishable.

Description

Cranidium somewhat convex, wider than long, with slightly downsloping fixed cheek; glabella large, unfurrowed, moderately elevated above genal region, a little constricted (tr.) medially and pointed anteriorly, surrounded by narrow and shallow axial furrows; it occupies ∽78% of the total length of the cranidium; occipital brim extremely narrow (sag.), delimited by a shallow, transverse furrow; anterior cephalic border convex, slightly widened sagittally, length (sag.) approximately half the length of preglabellar field, differentiated by change in slope of exoskeleton; preglabellar field depressed, with lateral margins moderately divergent; anterior facial suture somewhat divergent forward; posterior facial suture transverse, strongly directed outward; posterior fixigena very wide (tr.) and short (exsag.), with a shallow border furrow and a slender (exsag.), convex posterior border; palpebral area of the fixigena too poorly preserved for description. Available cranidium 14.5 mm long (sag.).

Librigenae, hypostome and thorax unknown.

Pygidium semicircular in outline, flat to somewhat convex transversely and longitudinally, width approximately twice length, margin entire; axis long and very narrow, hardly elevated above level of pleural fields, surrounded by narrow axial furrows, ∽15%–17% of total width of pygidium at anterior extremity, slightly tapered at anterior half and nearly parallel sided at posterior half, with marked anterior five rings and extremely faint or indistinct posterior four rings, ending in blunt point; length of axis ∽81%–83% of that of pygidium on sagittal line; articulating half-ring narrow (sag.), crescentic; pleural fields flat or weakly convex, crossed by five straight to slightly curved, oblique pleural furrows ending at level of the doublural margin; doublure wide, covered with 14 terrace lines; the anterior part of the doublural margin is slightly crenulate (Fig. 9.8); paradoublural line indistinguishable; some specimens show a well-defined, fairly flat pygidial border of uniform width (Fig. 9.5, 9.7, 9.8), which represents only 6%–8% of the total pygidial length (sag.). Largest observed pygidium 19.5 mm long (sag.).

Etymology

Refers to the Iruya area, Salta Province, Argentina.

Types

Holotype, pygidium, MLP 35158a (Fig. 9.3), length 7 mm; paratypes, one cranidium and seven pygidia (MLP 35043a, 35053b, 35154, 35156a, 35159–35161, 35163).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

The specimens described above show a long glabella, a posteriorly located palpebral area of the fixigena, a very wide (tr.) and short (exsag.) posterior fixigena, a narrow pygidial axis, and vestiges of an undulating doublural margin. Thus, they are allied to Ogygiocaris Angelin, Reference Angelin1854, which was previously described from the Middle Ordovician of Scandinavia and Great Britain, as well as from the upper Tremadocian of northwestern Argentina (e.g., Harrington and Leanza, Reference Harrington and Leanza1957; Henningsmoen, Reference Henningsmoen1960; Fortey and Owens, Reference Fortey and Owens1978; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2006 and references; Hansen, Reference Hansen2009). However, the pygidia studied exhibit only nine axial rings and five pairs of pleural furrows which are shallow and not distally curved, so the generic affinity is tentative.

The pygidia of both Ogygiocaris? iruyensis n. sp. and O. araiorhachis Harrington and Leanza, Reference Harrington and Leanza1957 sensu Waisfeld and Vaccari (Reference Waisfeld and Vaccari2006), from the upper Tremadocian of the Incamayo area, Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, figs. 71.1–71.3, 71.6, 72.2; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003, pl. 23, figs. 16, 17; 2006, fig. 1.A–I), show a very slightly undulating anterior doublural margin, which is more evident in well preserved specimens, and lack paradoublural lines. Nevertheless, O.? iruyensis differs in possessing slightly more divergent anterior branches of the facial sutures, an anteriorly pointed glabella, and a smaller number of pygidial axial rings and pleural furrows.

The new species most closely resembles “Thysanopyge”? latelimbata Harrington and Leanza (Reference Harrington and Leanza1957, fig. 84.1) and a group of pygidia of “Ogygiocaris araiorhachis” (Harrington and Leanza, Reference Harrington and Leanza1957, figs. 71.4, 71.5, 72.2, 72.3; see Waisfeld and Vaccari, Reference Waisfeld and Vaccari2006, p. 733), from the upper Tremadocian of the Cordillera Oriental. O.? iruyensis is distinguished by its slightly pointed preglabellar furrow, the wider (tr.) glabella, its less divergent anterior facial sutures, and its fewer pygidial axial rings and pleural furrows.

The type species, Ogygiocaris dilatata (Brünnich, Reference Brünnich1781) from the Middle Ordovician of Norway (Henningsmoen, Reference Henningsmoen1960, pl. 1, figs. 1–7, pl. 2, figs. 1–6; Hansen, Reference Hansen2009, pl. 1, figs. 1–8), differs from O.? iruyensis in having a larger pygidium with 11 discrete axial rings, 7 deep pleural furrows, an apparent paradoublural line, and a clear indentation on the posterior margin. Similarly, many other species of Ogygiocaris (O. debuchii [Brongniart, Reference Brongniart1822]; O. sarsi Angelin, Reference Angelin1854; O. striolata Henningsmoen, Reference Henningsmoen1960; O. seavilli Whittard, Reference Whittard1964; O. macrops Rushton and Hughes, Reference Rushton and Hughes1981; O. henningsmoeni Hansen, Reference Hansen2009) can be distinguished by having a conspicuous paradoublural line, a longer pygidial axis, and prominent pygidial pleural furrows, which are generally more numerous, longer and deeper than those of O.? iruyensis and show backwardly flexed extremities (Henningsmoen, Reference Henningsmoen1960; Whittard, Reference Whittard1964; Hughes, Reference Hughes1979; Rushton and Hughes, Reference Rushton and Hughes1981).

Subfamily Niobinae Jaanusson (in Moore, Reference Moore1959)

Genus Niobe Angelin, Reference Angelin1854

Subgenus Niobe (Niobella) Reed, Reference Reed1931

Type species

Niobe homfrayi Salter, Reference Salter1866, from the lower Tremadocian of North Wales, by original designation.

Niobe (Niobella) inflecta (Harrington and Leanza, Reference Harrington and Leanza1957) new combination

Figure 9.9–9.13

1957 Hypermecaspis inflecta Reference Harrington and LeanzaHarrington and Leanza, p. 125, fig. 48.1, 48.2.

Holotype

Pygidium from the lower Tremadocian of the Santa Victoria area, Cordillera Oriental, Argentina (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 48.2).

Description

Cranidium large, subtrapezoidal in outline, wider than long; glabella scarcely raised above level of fixigena, elongate, well defined by narrow axial furrows, widest posteriorly, narrowest at midlength and sub-truncate in front, occupying ∽88% of the total cranidial length; median glabellar node very weak, situated at level of the posterior end of the palpebral area; occipital ring narrows (sag.) medially, occupying 10% of the total glabellar length (sag.); occipital furrow shallow at sides and deepest on midline, curved backward medially; frontal area depressed, lacking differentiated border furrow, covered with sinuous terrace ridges subparallel to anterior cranidial margin; anterior facial suture diverging at an angle of 45º to the exsagittal line; posterior fixigenae wide (tr.), defined by sigmoidal sutures, with a distinct border furrow; palpebral area of the fixigena not preserved for description. Largest observed cranidium 34 mm long (sag.).

Materials

Two incomplete cranidia and four pygidia (MLP 35042c, 35050b, 35054, 35089b, 35094, 35109) from the Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Harrington and Leanza (Reference Harrington and Leanza1957, p. 125, fig. 48.1, 48.2) erected Hypermecaspis inflecta on the basis of a set of large pygidia (holotype 25 mm length) from the Santa Victoria area (Cordillera Oriental) which, according to Ebbestad (Reference Ebbestad1999, p. 32), differ from those of other species of Hypermecaspis Harrington and Leanza, Reference Harrington and Leanza1957 in having a semicircular outline and a less tapering rachis, which is bluntly rounded posteriorly. Ebbestad (Reference Ebbestad1999) tentatively reassigned H. inflecta to Cermatops Shergold, Reference Shergold1980, and pointed out its high degree of similarity with the pygidium of C. thalastus Jell, Hughes and Brown, Reference Jell, Hughes and Brown1991, from the Furongian of western Tasmania (Jell et al., Reference Jell, Hughes and Brown1991, fig. 7F–H).

The cranidium of “H”. inflecta (Fig. 9.9, 9.10) is described herein for the first time, which allowed for a further understanding of the affinities of this species. Although the material examined is scarce, it clearly shows a smooth, flat frontal area, and palpebral lobes extremely close to the glabella. Therefore, its general aspect suggests closer correspondence with Niobe (Niobella) Reed, Reference Reed1931; a taxon characterized by having a depressed frontal area; gently divergent anterior branches of facial sutures; a straight-sided or slightly constricted, non-bacculate glabella; palpebral lobes placed in contact with the axial furrow; and a flat pygidial border (e.g., Whittington, Reference Whittington1965; Shergold and Sdzuy, Reference Shergold and Sdzuy1984; Peng, Reference Peng1990b). Following Ebbestad (Reference Ebbestad1999 and references), we recognize Niobella at subgeneric level.

Niobe (Niobella) inflecta most closely resembles N. (N.) shenjiawanensis Peng, Reference Peng1990b, from the lower Tremadocian (Onychopyge-Hysterolenus Assemblage Zone) of China (Peng, Reference Peng1990b, pl. 12, figs. 6, 7), which was originally based on three cranidia showing a long (sag.), medially constricted glabella, gently divergent anterior facial sutures, a moderately developed frontal area, and oblique posterior facial sutures. The Argentinian species differs in having a better defined occipital furrow.

Genus Metayuepingia Liu in Zhou et al., Reference Zhou, Liu, Meng and Sun1977

Type species

Metayuepingia angustilimbata Liu in Zhou et al., Reference Zhou, Liu, Meng and Sun1977 from the Lower Ordovician of China, by original designation.

Metayuepingia riccardii new species

Figure 10.1–10.27

Figure 10 Metayuepingia riccardii n. sp. from the Santa Rosita Formation in the Iruya area, northwestern Argentina: (1) cranidium, latex cast of specimen figured in (2) MLP 35070, ×2.5; (2) cranidium, MLP 35070, ×2.5; (3) cranidium, latex cast of specimen figured in (4) MLP 35048, ×2.5; (4) cranidium (holotype) MLP 35048, ×2.5; (5) cranidium, MLP 35401, ×2.5; (6) cranidium, latex cast, MLP 35042a, ×2.5; (7) librigena, latex cast, MLP 35126, ×2.5; (8) librigena, MLP 35155, ×3.5; (9) hypostome, MLP 35146, ×2.5; (10) hypostome, MLP 35081, ×2.5; (11) cranidium, MLP 35087, ×2.5; (12) pygidium, MLP 35073a, ×2.1; (13) pygidium, MLP 35136, ×2.1; (14) fragmentary thoracopygon, latex cast, MLP 35058, ×1.7; (15) pygidium, latex cast, MLP 35057a, ×2.1; (16) pygidium, latex cast, MLP 35085, ×2.1; (17) pygidium, latex cast, MLP 35089a, ×1.7; (18) pygidium, MLP 35071, ×2.1; (19) pygidium, MLP 35086, ×2.1; (20) pygidium, MLP 35039, ×2.1; (21) pygidium, MLP 35063, ×2.1; (22) pygidium, MLP 35093, ×1.7; (23) pygidium, latex cast, MLP 35044, ×2.1; (24) pygidium, MLP 35045, ×2.1; (25) pygidium, MLP 35082, ×2.1; (26) pygidium, latex cast, MLP 35056a, ×2.1; (27) pygidium, MLP 35092a, ×2.1. All specimens from Pantipampa.

Diagnosis

A species of Metayuepingia with an oblique posterior facial suture, a poorly defined posterior cranidial border, a tapering pygidial axis with five to six rings, and a proportionately wide pygidial border.

Description

Cranidium subtrapezoidal in outline, gently convex, with concave frontal area and pointed anterior margin; glabella elongate, unfurrowed, slightly constricted (tr.) at level of palpebral areas, surrounded by shallow and narrow axial furrows, ill-defined anteriorly where it grades into preglabellar field; it occupies approximately four-fifths length of cranidium and a half of maximum cranidial width (tr.); median glabellar node delicate, situated opposite posterior part of palpebral lobes; occipital brim extremely narrow (sag.), delimited by a faint band furrow; anterior facial suture slightly diverging in front of eyes, meeting mesially in pointed ogive; palpebral area of the fixigena narrow (tr.); palpebral lobe prominent, arcuate, situated behind cranidial midpoint, occupying ∽23%–25% of the total length (sag.) of the cranidium; posterior facial suture oblique backward and outward, sigmoidal; posterior fixigena wide (tr.), triangular; librigenae with wide, concave lateral border and rounded genal angle; posterior border furrow weak; hypostome with wide (tr.) lateral borders, covered with terrace lines. Largest observed cranidium 15 mm long (sag.).

Pygidium sub-semicircular in outline, gently to moderately convex transversely and longitudinally, wider than long; axis evenly tapering backward, scarcely elevated above level of pleural fields, surrounded by narrow axial furrows, with slightly marked five to six rings and terminal piece, rounded at posterior end; it occupies ∽25% of total width of pygidium at anterior extremity, and 69%–71% of length of pygidium on sagittal line; pleural fields moderately convex, smooth; border broad, concave, not well defined by border furrows; doublure very wide, covered with 12 terrace ridges following the doublural contour. Largest observed pygidium 18.5 mm long (sag.).

Etymology

Dedicated to Dr Alberto C. Riccardi (Museo de La Plata).

Types

Holotype, cranidium, MLP 35048 (Fig. 10.4), length 11.3 mm; paratypes, 13 cranidia, 8 librigenae, 4 hypostomes, 1 fragmentary thoracopygon and 24 pygidia (MLP 35034b, 35036a, 35038, 35039, 35041, 35042a, 35043b, 35044, 35045, 35047, 35055a, 35056a, 35057a, 35058, 35063, 35069, 35070, 35071, 35073a, 35076a, 35081, 35082, 35083b, 35085–35087, 35089a, 35092a, 35093, 35099, 35101b, 35108, 35113b, 35116, 35122, 35126, 35134, 35136, 35137, 35139, 35146, 35151, 35152, 35155, 35157a, 35401).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

The presence of a large, medially constricted glabella; a glabellar node located opposite posterior part of palpebral lobes; an absent occipital furrow; prominent and medially placed palpebral lobes; an anteriorly up-turned frontal area; an isoteliform facial suture; a tapering, segmented pygidial axis; smooth pleural fields; and a broad concave pygidial border are characters of Metayuepingia Liu in Zhou et al., Reference Zhou, Liu, Meng and Sun1977, a taxon previously described from the Lower Ordovician of China (Zhou et al., Reference Zhou, Liu, Meng and Sun1977; Peng, Reference Peng1990b). Although the pygidial axis of the material studied is slightly longer, and the pygidial border is somewhat wider than those of other species of Metayuepingia, we feel that these variations lack generic significance.

Metayuepingia latilimbata Liu in Zhou et al., Reference Zhou, Liu, Meng and Sun1977, from the upper Tremadocian (Shumardia (Conophrys) acutifrons-Asaphopsoides Zone) of China (Zhou et al., Reference Zhou, Liu, Meng and Sun1977, pl. 64, figs. 5, 6; Peng, Reference Peng1990b, pl. 14, figs. 12–16), differs from M. riccardii in having a transverse posterior facial suture, a better defined posterior border of the fixigena, a slightly shorter (sag.) pygidial axis with four rings and terminal piece, and a proportionately narrower pygidial border. The type species, Metayuepingia angustilimbata Liu in Zhou et al., Reference Zhou, Liu, Meng and Sun1977, from the Tremadocian (Apatokephalus latilimbatus-Taoyuania affinis and Shumardia [Conophrys] acutifrons-Asaphopsoides zones) of China (Zhou et al., Reference Zhou, Liu, Meng and Sun1977, pl. 64, figs. 1–3; Peng, Reference Peng1990b, pl. 13, figs. 10–13; pl. 14, figs. 1–11) shows, in addition, a less tapered pygidial axis.

Metayuepingia divergens Peng, Reference Peng1990b, from the upper Tremadocian (Shumardia [Conophrys] acutifrons-Asaphopsoides Zone) of China (Peng, Reference Peng1990b, pl. 15, figs. 2, 3), was described on the basis of two distorted cranidia which differ from M. riccardii in having a more divergent anterior facial suture, a wider (tr.) anterior fixigena, and a gently convex frontal area.

Superfamily Remopleuridioidea Hawle and Corda, Reference Hawle and Corda1847

Family Richardsonellidae Raymond, Reference Raymond1924

Genus Kainella Walcott, Reference Walcott1925

Type species

Hungaia billingsi Walcott, Reference Walcott1924, from the lower Survey Peak Formation in British Columbia, Canada, by original designation.

Kainella meridionalis Kobayashi, Reference Kobayashi1935

Figure 11.22, 11.23

Figure 11 Richardsonellids from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–21) Kainella teiichii Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010: (1) librigena, MLP 35353a, ×1.4, Rodeo Colorado (RC); (2) cranidium, latex cast, MLP 35240, ×1.4, Pantipampa (P); (3) cranidium, latex cast, MLP 35179, ×1.6, P; (4) cranidium, MLP 35317, ×2.5, RC; (5) fragmentary cranidium, MLP 35319a, ×1.4, RC; (6) cranidium, latex cast, MLP 4929, ×1.9, RC; (7) fragmentary cranidium, MLP 35254, ×1.4, P; (8) cranidium, MLP 4942, ×1.4, RC; (9) cranidium, MLP 4970, ×1.4, RC; (10) cranidium, latex cast, MLP 35333, ×2.2, RC; (11) pygidium, MLP 4954, ×1, RC; (12) pygidium, MLP 35227, ×1.8, P; (13) pygidium, MLP 35326, ×1.6, RC; (14) pygidium, latex cast, MLP 35189a, ×2.2, P; (15) pygidium, latex cast, MLP 35354, ×2.2, RC; (16) pygidium, MLP 35088, ×2.2, P; (17) pygidium, MLP 35164, ×1.6, P; (18) pygidium, MLP 4960, ×1.6, RC; (19) pygidium, MLP 4935, ×2.2, RC; (20) pygidium, MLP 4959, ×2.2, RC; (21) pygidium, MLP 35331, ×2.2, RC. (22, 23) Kainella meridionalis Kobayashi, Reference Kobayashi1935: (22) cranidium, MLP 35021, ×1.7, P; (23) fragmentary cranidium, MLP 34966, ×1.7, P.

1935 Kainella meridionalis Reference KobayashiKobayashi, p. 65, pl. 11, figs. 5–7 (only).

1957 Kainella meridionalis; Reference Harrington and LeanzaHarrington and Leanza, p. 127, fig. 50.1–50.8.

2010 Kainella meridionalis; Reference Vaccari and WaisfeldVaccari and Waisfeld, p. 275, figs. 1.1–1.3, 2.1–2.14, 3, 9.22 (see for further synonymy).

Lectotype

Cranidium from the lower Tremadocian of the Incamayo area, Cordillera Oriental, Argentina (Kobayashi, Reference Kobayashi1935, pl. 11, fig. 7; Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010, fig. 1.2).

Materials

Three fragmentary cranidia and one pygidium (MLP 34965–34967, 35021) from the lower part of the Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella meridionalis Zone and basal K. teiichii Zone.

Remarks

Vaccari and Waisfeld (Reference Vaccari and Waisfeld2010) emended the diagnosis and scope of Kainella meridionalis Kobayashi, Reference Kobayashi1935 from northwestern Argentina, and regarded the presence of four pairs of anastomosing ridges on the preglabellar field as one of its most characteristic features. Since Kainella specimens from the lower part of the Pantipampa section show this character, they are assigned confidently to this species. Vaccari and Waisfeld (Reference Vaccari and Waisfeld2010) discussed the affinities of K. meridionalis with other species of Kainella from the Cordillera Oriental of Argentina and Bolivia (e.g., K. teiichii Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010, see below; K. andina Suárez-Soruco, Reference Suárez Soruco1975; K. morena Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010), North America, Korea, China, and New Zealand.

Kainella teiichii Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010

Figure 11.1–11.21

2010 Kainella teiichii Reference Vaccari and WaisfeldVaccari and Waisfeld, p. 278, figs. 1.5, 4.1–4.14, 5 (see for further synonymy).

Holotype

Pygidium from the Tremadocian of the Tilcara area, Cordillera Oriental, Argentina (Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010, fig. 4.13).

Materials

Thirty cranidia, eighteen librigenae and twenty pygidia (MLP 4929, 4935, 4942, 4954, 4959, 4960, 4970, 34977c, 34987a, 35060, 35066, 35072, 35080, 35088, 35090, 35105a, 35107, 35125, 35164, 35179, 35182, 35187, 35189a, 35202a, 35203, 35204, 35208, 35225–35228, 35231–35234, 35236, 35237, 35240, 35247, 35249, 35250, 35254, 35255, 35268, 35271, 35272b, 35307, 35310, 35317, 35318d, 35319a, 35326, 35328–35331, 35333, 35334, 35337, 35340–35342, 35349b, 35353a, 35354) from the Pantipampa and lower Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, Tremadocian, Kainella teiichii Zone.

Remarks

The specimens examined represent a distinctive Kainella species of the upper Pantipampa and lower Rodeo Colorado sections. They are characterized by having a single pair of well-defined oblique ridges on the preglabellar field, slightly curved genal spines, a pygidial axis ∽1.5 times longer than wide, and backwardly oblique pygidial pleural furrows. Therefore, according to the diagnosis of Vaccari and Waisfeld (Reference Vaccari and Waisfeld2010), they are assignable to Kainella teiichii. This species is very similar to K. meridionalis Kobayashi, Reference Kobayashi1935, from the lower Tremadocian of the Cordillera Oriental, but the latter differs mainly by showing anastomosing preglabellar ridges, more strongly curved genal spines, and a proportionately longer (sag.) pygidial axis (Vaccari and Waisfeld, Reference Vaccari and Waisfeld2010). Kainellids collected from Rodeo Colorado by Figueroa Caprini (Reference Figueroa Caprini1955) were added to the present study (Fig. 11.6, 11.8, 11.9, 11.11, 11.18, 11.19, 11.20; see also Tortello et al., Reference Tortello, Esteban and Aceñolaza2002, fig. 5.E–H) and assigned to K. teiichii.

Genus Pseudokainella Harrington, Reference Harrington1938

Type species

Pseudokainella keideli Harrington, Reference Harrington1938, from the Tremadocian of the Cordillera Oriental, Argentina, by original designation.

Remarks

After the original description of Harrington (Reference Harrington1938) and Harrington and Leanza (Reference Harrington and Leanza1957), Pseudokainella was revised by Jell (Reference Jell1985), who regarded it as a kainellid having a preglabellar field of variable length, a variable angle of divergence of the anterior facial suture, and three, four, or five pairs of pygidial marginal spines which decrease in size posteriorly (see also Peng, Reference Peng1990b; Tortello and Esteban, Reference Tortello and Esteban2007). Thus, Elkanaspis Ludvigsen, Reference Ludvigsen1982 and Fatocephalus Duan and An in Guo et al., Reference Guo, Duan and An1982 could be considered as junior synonyms of Pseudokainella (Jell, Reference Jell1985).

Alternatively, Ludvigsen (Reference Ludvigsen1982) and Ludvigsen et al. (Reference Ludvigsen, Westrop and Kindle1989) prefer to limit Pseudokainella to species having a particularly short (sag.) preglabellar field, a widely divergent anterior facial suture, and a very long anterior pair of pygidial spines. In accordance with this criterion, Waisfeld and Vaccari (Reference Waisfeld and Vaccari2003) restricted the concept of Pseudokainella to the type species P. keideli Harrington.

Pseudokainella keideli Harrington, Reference Harrington1938

Figure 12.1–12.6

Figure 12 Richardsonellids and kainellids from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–6) Pseudokainella keideli Harrington, Reference Harrington1938: (1) cranidium, MLP 35180, ×2.3, Pantipampa (P); (2) cranidium, MLP 35197, ×2.3, P; (3) cranidium, MLP 35264, ×2.3, P; (4) cranidium, MLP 35265, ×2.3, P; (5) librigena, MLP 35194a, ×2.3, P; (6) posterior thorax and pygidium, MLP 35297, ×2.3, P. (7–13) Apatokephalus rugosus n. sp.: (7) cranidium (holotype) MLP 35322, ×3.4, Rodeo Colorado (RC); (8) detail of glabellar granulation, latex cast, MLP 35322, ×6.9, RC; (9) detail of glabellar granulation, latex cast, MLP 35186b, ×6.8, P; (10) librigena, MLP 35186a, ×3.4, P; (11) small cranidium, MLP 35186b, ×4.5, RC; (12) cranidium, latex cast, MLP 35150, ×3.4, P; (13) pygidium, MLP 35130a, ×3.4, P.

1938 Pseudokainella keideli Reference HarringtonHarrington, p. 174, pl. 5, figs. 11–15.

1957 Pseudokainella keideli; Reference Harrington and LeanzaHarrington and Leanza, p. 131–132, figs. 51, 52.5–52.10.

2003 Pseudokainella keideli; Reference Waisfeld and VaccariWaisfeld and Vaccari, p. 325, pl. 27, figs. 13–16.

2005 Pseudokainella keideli; Reference Zeballo and TortelloZeballo and Tortello, p. 139, figs. 5G–H.

Holotype.—Complete specimen from the Tremadocian of the Tilcara area, Cordillera Oriental, Argentina (Harrington, Reference Harrington1938, pl. 5, fig. 14; Harrington and Leanza, Reference Harrington and Leanza1957, fig. 52.6).

Materials

One cephalon, twenty cranidia, one librigena and fifteen pygidia (MLP 4926, 4927, 4952a, 35178, 35180, 35182, 35193, 35194a, 35195–35198, 35229, 35230, 35264, 35265, 35274, 35277, 35281, 35283a, 35292–35297, 35299, 35300, 35323c, 35339, 35343, 35345, 35347) from the Pantipampa and Rodeo Colorado localities, Iruya area, northwestern Argentina, Santa Rosita Formation, Tremadocian, Kainella teiichii and Bienvillia tetragonalis zones.

Remarks

As stated by Harrington and Leanza (Reference Harrington and Leanza1957), Pseudokainella keideli Harrington is characterized by having a long and conical glabella with 2 or 3 oblique lateral furrows, an extremely short (sag.) preglabellar field, strongly divergent anterior branches of facial sutures, narrow (tr.) palpebral area of the fixigena, genal angles in a slightly advanced position, a tapering pygidial axis composed of four rings and a terminal piece, and four pairs of pygidial marginal spines, among which the anterior pair is much longer than the others. Although the material studied herein is not perfectly preserved, it shows such diagnostic features and is therefore assigned to this species.

Pseudokainella keideli has been previously described from the Bienvillia tetragonalis Zone of the Tilcara region (Harrington, Reference Harrington1938; Harrington and Leanza, Reference Harrington and Leanza1957; Waisfeld and Vaccari, Reference Waisfeld and Vaccari2003; Zeballo and Tortello, Reference Zeballo and Tortello2005). This report provides the first record from the northern Cordillera Oriental, from both the Kainella teiichii Zone and the Bienvillia tetragonalis Zone.

Family Kainellidae Ulrich and Resser, Reference Ulrich and Resser1930

Genus Apatokephalus Brøgger, Reference Brøgger1896

Type species

Trilobites serratus Boeck, Reference Boeck1838, from the upper Tremadocian in Oslo, Norway (subsequently designated by Bassler, Reference Bassler1915).

Remarks

Ebbestad (Reference Ebbestad1999) discussed in detail the concept of the cosmopolitan genus Apatokephalus Brøgger, Reference Brøgger1896 and redescribed the type species A. serratus (Boeck, Reference Boeck1838) based on well-preserved material from Norway. Apatokephalus is characterized by having a bell-shaped glabella with a long (sag.) frontal lobe, three pairs of lateral furrows, large palpebral lobes very close to the glabella, librigenal spines in an advanced position, and a small, serrate pygidium (Peng, Reference Peng1990b). The numerous species of this genus show variations in the length (sag.) of the preglabellar field, the outline of the glabellar furrows, the sculpture of the glabella, and the direction of the anterior and posterior facial sutures (Peng, Reference Peng1990b; Ebbestad, Reference Ebbestad1999).

Apatokephalus rugosus new species

Figure 12.7–12.13

Diagnosis

A species of Apatokephalus with a sculpture of raised granules of different sizes on the test, a very short (sag.) preglabellar field, sigmoidal anterior facial sutures curving backward laterally, and a pygidium with four pairs of apparent pleural furrows and five broad-based marginal spines.

Description

Cranidium with slightly pointed anterior margin; glabella bell-shaped, moderately convex, slightly rounded anteriorly, occupying ∽86% of the total cranidial length, clearly expanded (tr.) between palpebral lobes; frontal glabellar lobe subquadrate, occupying approximately one-fourth of the glabellar length; lateral glabellar furrows distinct, medially disconnected, only anterior two pairs connecting with axial furrows; S1 long, sigmoidal, directed obliquely inward and backward, situated opposite middle (sag.) of palpebral lobes; S2 straight to slightly curved backward, approximately parallel to the preoccipital furrow; S3 shorter than S1 and S2, transverse, straight to slightly curved forward; occipital furrow distinct, of uniform depth, slightly curved forward medially and laterally; occipital ring somewhat wider (tr.) than the anterior lobe of the glabella, broadly rounded posteriorly, occupying ∽18% of the total glabellar length; preglabellar field very short (sag.), depressed; anterior cranidial border much longer (sag.) than preglabellar field, upturned, with open-spaced terrace ridges subparallel to margin, separated from the preglabellar field by a pitted border furrow; anterior sections of facial suture sigmoidal, curving backward laterally; palpebral lobes large, crescentic, extending from the occipital furrow to the third lateral glabellar lobe (L3); palpebral lobe furrow deeply incised; librigenae with long genal spines continuing curvature of lateral margins; genal angles moderately advanced; eye socle semi-circular, very narrow, elevated above flat genal field; posterior facial suture transverse, extending outward from posterior end of eye socle; lateral cephalic border with 5–6 fine terrace lines subparallel to margin, delimited by a shallow border furrow; external surface of exoskeleton covered with variably developed raised tubercules, which are less distinct on the small holaspides (Fig. 12.11). Largest observed cranidium 8.8 mm long (sag.).

Pygidium semielliptical in outline, approximately twice as wide (tr.) as long (sag.); axis transversely convex, tapering backward, well defined by discrete axial furrows, divided into four rings and a triangular terminal piece that continues backward into a weak posterior ridge, occupying ∽80% of the total pygidial length (excluding articulating half ring) and one-third of the maximum pygidial width; articulating half ring very narrow (sag.), delimited by a conspicuous furrow; pleural fields only slightly downsloping, with four pairs of distinct pleural furrows and five pairs of broad-based lateral spines derived from pleurae, which decrease in size posteriorly; doublure wide, covered with 10–12 terrace lines; external surface of axial rings and pleural fields with densely spaced tubercles. Largest observed pygidium 5 mm long (sag.).

Etymology

Latin rugosus, referring to the sculpture of the exoskeleton.

Types

Holotype, cranidium, MLP 35322 (Fig. 12.7), length 8.8 mm; paratypes, six cranidia, three librigenae, and three pygidia (MLP 35057c, 35076b, 35078, 35114, 35123, 35130a, 35131, 35150a, 35186a,b, 35353b).

Occurrence

Pantipampa and Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

The specimens examined exhibit a variably developed sculpture on the external surface of the test. Small cranidia show sparse openly spaced granules (Fig. 12.11), whereas late holaspides have larger tubercles, which are of different sizes and more or less densely packed (compare Fig. 12.7–12.9 and 12.12).

Apatokephalus rugosus closely resembles A. sarculum Fortey and Owens, Reference Fortey and Owens1991, from the upper Tremadocian of north England (Fortey and Owens, Reference Fortey and Owens1991, fig. 12.a–j, l, o), mainly in having a surface sculpture of distinct granules, well-defined glabellar furrows, a short (sag.) preglabellar field, and a sigmoidal and transverse facial suture. However, A. sarculum differs in its much shorter (sag.) pygidial axis. Apatokephalus canadensis Kobayashi, Reference Kobayashi1953, from the Tremadocian of western Canada (Kobayashi, Reference Kobayashi1953, pl. 3, figs. 1–4; Dean, Reference Dean1989, pl. 24, figs. 6, 9), exhibits a well-developed ornamentation and a very short preglabellar field, but differs from A. rugosus in lacking broad-based pygidial spines.

The type species Apatokephalus serratus (Boeck, Reference Boeck1838), from the upper Tremadocian of Norway (Fortey and Owens, Reference Fortey and Owens1991, fig. 12k, m, p, q; Ebbestad, Reference Ebbestad1999, figs. 41A, 42A–O), differs from A. rugosus in having a glabella covered with more prominent and more openly spaced tubercles, and six pairs of delicate marginal spines on the pygidium. The pygidium of Apatokephalus exiguus Harrington and Leanza, Reference Harrington and Leanza1957, from the upper Tremadocian of the Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, figs. 57, 58.1–58.5), is distinguished from that of A. rugosus mainly in its shorter (sag.) axis and its minute marginal spines.

Apatokephalus tibicen Přibyl and Vanĕk, Reference Přibyl and Vanĕk1980, from the upper Tremadocian of the Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 56.1, 56.3–56.8, 56.10; Přibyl and Vanĕk, Reference Přibyl and Vanĕk1980, pl. 12, figs. 3, 4; Tortello and Esteban, Reference Tortello and Esteban2014, figs. 9.11–9.15, 9.19), is distinguished from A. rugosus mainly by its longer (sag.) preglabellar field. In addition, the anterior facial suture is transverse or strongly diverging forwardly in A. tibicen, while it curves backward laterally in A. rugosus.

Apatokephalus levisensis (Rasetti, Reference Rasetti1943), from the lower Ordovician of Quebec, eastern Canada (Fortey and Owens, Reference Fortey and Owens1991, fig. 12n, r), differs from A. rugosus in the presence of a longer (sag.) preglabellar field. The preglabellar field is even larger in A. longifrons Dean, Reference Dean1989, from the Tremadocian of Canada (Dean, Reference Dean1989, pl. 24, figs. 1, 2, 4, 7), and Apatokephalus sp. (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 9.16, 9.20), from the upper Tremadocian of the Nazareno area, Cordillera Oriental.

Apatokephalus latilimbatus Peng, Reference Peng1990b, from the Tremadocian of China (Peng, Reference Peng1990b, pl. 11, figs. 1–14, pl. 12, figs. 4, 5, 9), further differs from A. rugosus in its wider (sag.) anterior border, its strongly advanced genal spines, and its smaller pygidial axis. Apatokephalus dubius (Linnarsson, Reference Linnarsson1869), from the upper Tremadocian of Scandinavia (Ebbestad, Reference Ebbestad1999, figs. 41B, 42A–G), is distinguished mainly by having a fine fingerprint-like ornament on the glabella. Similarly, the skeleton of A. incisus Dean, Reference Dean1966, from the Lower Ordovician of the Montagne Noire, southern France, lacks tuberculate sculpture.

Family Ceratopygidae Linnarsson, Reference Linnarsson1869

Genus Onychopyge Harrington, Reference Harrington1938

Type species

Onychopyge riojana Harrington, Reference Harrington1938, from the upper Furongian of La Rioja Province, Argentina, by original designation.

Remarks

Although the original diagnosis of Onychopyge was based on very fragmentary material from Argentina (Harrington, Reference Harrington1938; Harrington and Leanza, Reference Harrington and Leanza1957), the concept of the genus was later improved with new and better preserved material mainly from Mexico (Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968), Australia (Jell, Reference Jell1985) and China (Qian, Reference Qian1986). Onychopyge has exceptionally large palpebral lobes with their inner ends adjacent to axial furrows, a subrectangular glabella with faint to moderately developed lateral furrows, a tapered pygidial axis of five to seven rings extended into a postaxial ridge, and a large anterior pygidial segment showing a pair of wide pleural furrows and a pair of prominent marginal spines. Posterior pleural furrows of the pygidium are faint or absent (Harrington and Leanza, Reference Harrington and Leanza1957; Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968; Jell, Reference Jell1985).

The material of Onychopyge described to date from Argentina comes from the upper Furongian (Parabolina frequens argentina Zone) of both the Famatina Range (Harrington, Reference Harrington1938; Harrington and Leanza, Reference Harrington and Leanza1957; Tortello and Esteban, Reference Tortello and Esteban2007) and the Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957; Benedetto, Reference Benedetto1977; Zeballo and Tortello, Reference Zeballo and Tortello2005; Esteban and Tortello, Reference Esteban and Tortello2007). The first Tremadocian material is described below.

Onychopyge acenolazai new species

Figure 13.1–13.13

Figure 13 Ceratopygids and hapalopleurids from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–13) Onychopyge acenolazai n. sp.: (1) cranidium, MLP 35040, ×2.5, Pantipampa (P); (2) cranidium (holotype) MLP 35091, ×2.7, P; (3) cranidium, MLP 35096, ×2.7, P; (4) fragmentary cranidium, MLP 35074b, ×2.7, P; (5) cranidium, MLP 35166, ×2.5, P; (6) pygidium, MLP 35117, ×2.7, P; (7) pygidium, latex cast, MLP 35167, ×2.4, P; (8) pygidium, MLP 35075b, ×2.7, P; (9) pygidium, latex cast, MLP 35059a, ×2.7, P; (10) pygidium, latex cast, MLP 35119, ×2.7, P; (11) pygidium, latex cast, MLP 35118, ×2.7, P; (12) pygidium, MLP 35097, ×2.7, P; (13) detail of pygidial surface, latex cast, MLP 35167, ×5. (14–20) Onychopyge gonzalezae n. sp.: (14) cranidium, MLP 35079, ×3.5, P; (15) pygidium, latex cast, MLP 35143, ×2.7, P; (16) pygidium (holotype) MLP 35147, ×2.7, P; (17) cranidium, MLP 35049a, ×2.7, P; (18) pygidium, MLP 35046, ×2.7, P; (19) pygidium, MLP 35064, ×2.7, P; (20) pygidium, latex cast, MLP 35124, ×2.7, P. (21–27) Ceratopygidae gen. et sp. indet.: (21) cranidium, latex cast, MLP 35319b, ×4.1, Rodeo Colorado (RC); (22) cranidium, MLP 35176, ×4.2, P; (23) cranidium, MLP 35181, ×4.3, P; (24) pygidium, MLP 35175, ×3.5, P; (25) cranidium, latex cast, MLP 35127b, ×4.3, P; (26) cranidium, MLP 35318a, ×4.3, RC; (27) pygidium, MLP 4961a, ×4.3, RC. (28) Hapalopleura sp. indet.: cranidium, latex cast, MLP 35111, ×2.7, P.

Diagnosis

A species of Onychopyge with a laterally expanded frontal glabellar lobe, a frontal area bounded posteriorly by a shallow accessory furrow which is interrupted by the anterior end of the glabella, a short (tr.) and bifurcate lateral glabellar furrow S1, and a strongly tapered pygidial axis of five rings and terminal piece. External surface of exoskeleton covered with Bertillon pattern of delicate lines.

Description

Cranidium of low convexity in both anterior and lateral profiles, subtrapezoidal in outline, as long as wide; glabella large, subrectangular in outline, longer than wide, slightly raised above level of fixigenae, delimited by sinuous axial furrows, clearly expanded (tr.) both at glabellar lateral lobe L2 and frontal lobe, with rounded anterolateral corners and slightly curved anterior margin, occupying ∽85%–88% of the total cranidial length, with a discrete lateral furrow S1 and extremely faint indications of S2 and S3; S1 disconnected at middle and separated from axial furrows, short, bifurcate, with greatest depth at point of adaxial bifurcation; glabellar median node very delicate, located in preoccipital segment; occipital furrow deepest at sides and shallow on midline, slightly curved backward medially; occipital ring wider (tr.) than the rest of the glabella, broadly rounded posteriorly, occupying ∽13% of the total glabellar length; anterior facial suture divergent before converging inward along the anterior cranidial margin; frontal area distinct, slightly convex, bounded posteriorly by a shallow, backwardly oblique brim furrow (=“accessory furrow”) that is interrupted by the anterior end of the glabella; palpebral lobes large, semicircular, approximately one-half length of glabella; palpebral furrows shallow but distinct; posterior limbs narrow (exsag.) and strap-like. Bertillon pattern of fine lines covers the external surface of the cranidium. Largest observed cranidium 15 mm long (sag.).

Librigenae fragmentary, insufficient for description. Hypostome and thorax unknown.

Pygidium subparabolic in ouline, wider than long, with slightly pointed posterior margin; axis convex, elevated above pleural fields, anterior width one third maximum width of pygidium, tapered backward, surrounded by narrow axial furrows, occupying ∽65%–70% of the total pygidial length (sag.); it is composed of a short (sag.) articulating half-ring, five rings and a terminal piece that are defined by shallow, forwardly curved transaxial furrows; a narrow postaxial ridge extends from the axis to the posterior pygidial margin; pleural fields weakly convex; anterior pleural furrow wide, extended posterolaterally into a pair of stout marginal spines; posterior pleural furrows indistinct; border furrow absent; doublure wide, carrying 10–12 fine, openly spaced terrace lines following the doublural contour; external surface of pygidium covered with Bertillon pattern of delicate lines. Largest observed pygidium 12.5 mm long (sag.).

Etymology

Dedicated to Dr Florencio G. Aceñolaza (Universidad Nacional de Tucumán).

Types

Holotype, cranidium, MLP 35091 (Fig. 13.2), length 12.4 mm; paratypes, nine cranidia, one fragmentary librigena, and eleven pygidia (MLP 35035d, 35040, 35059a, 35068a, 35074b, 35075b, 35083a, 35096, 35097, 35104, 35105b, 35117–35119, 35138, 35165–35167, 35169, 35191, 35201).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

The presence of a posteriorly located brim furrow, which is interrupted by the anterior end of the glabella, is one of the most diagnostic attributes of the new species Onychopyge acenolazai. Onychopyge parkerae Jell, Reference Jell1985, from the Tremadocian of Australia (Jell, Reference Jell1985, pl. 23, figs. 1–16, pl. 24, figs. 1–4), differs from O. acenolazai in having a brim furrow that is concurrent with the preglabellar furrow, and a shorter (sag.) pygidial axis, which occupies only a little more than half pygidial length. Onychopyge depressa Qian, Reference Qian1986, from the Cambrian–Ordovician boundary interval of China (Qian, Reference Qian1986, pl. 80, figs. 1–6, 11, text-fig. 116), also differs by its more anteriorly located brim furrow and, in addition, its better defined lateral glabellar furrows, the smaller palpebral lobes, and its much shorter (sag.) post-axial region.

As with many other species of the genus, Onychopyge austrina Peng, Reference Peng1984, from the lower Tremadocian of China (Peng, Reference Peng1984, pl. 6, figs. 1–3, pl. 7, figs. 1, 2; Peng, Reference Peng1990b, pl. 18, figs. 8–10), differs from O. acenolazai in lacking an apparent brim furrow. Besides, the former is distinguished by having a very narrow, abruptly upturned anterior cranidial border.

Onychopyge acenolazai is differentiated from the type species, Onychopyge riojana Harrington, Reference Harrington1938, from the upper Furongian of La Rioja, Argentina (Harrington, Reference Harrington1938, pl. 5, fig. 30; Harrington and Leanza, Reference Harrington and Leanza1957, figs. 95, 96.2a–c; Tortello and Esteban, Reference Tortello and Esteban2007, figs. 7.5–7.14), because the latter shows a less distinct preglabellar furrow, a longer (sag.) pygidial axis which is composed of seven segments instead of five, and noticeable posterior pleural furrows on the pygidium. Additionally, Onychopyge sp. aff. O. riojana, from the Tremadocian of New Zealand (Wright et al., Reference Wright, Cooper and Simes1994, fig. 15B–G), exhibits considerably smaller palpebral lobes.

Onychopyge acenolazai and O. argentina Harrington and Leanza, Reference Harrington and Leanza1957, from the upper Furongian of the Cordillera Oriental (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 96.1a–d), share a pygidium with a tapered axis of five segments, and an acutely rounded posterior margin. However, the cranidium of O. acenolazai shows a longer (sag.) frontal area, as well as more posteriorly located palpebral lobes. Onychopyge acenolazai differs from O. harringtoni Benedetto, Reference Benedetto1977, from the upper Furongian of the western Cordillera Oriental (Benedetto, Reference Benedetto1977, pl. 2, figs. 14, 15, text-fig. 10), in having a non-tapered glabella, indistinct glabellar lateral furrows S2 and S3, longer (exsag.) palpebral lobes, and five pygidial axial rings instead of six.

The exoskeleton of Onychopyge sculptura Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, from the upper Furongian-lower Tremadocian of Mexico (Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968, pl. 100, figs. 1–7, 10), exhibits a Bertillon pattern of raised lines which is very similar to that of O. acenolazai. Nevertheless, the Argentinian species differs by its non-tapered glabella, its more distinct preglabellar furrow, and its wider (tr.) pygidium. Onychopyge branisi Suárez-Soruco, Reference Suárez Soruco1975, from the lower Tremadocian of southern Bolivia (Suárez-Soruco, Reference Suárez Soruco1975, pl. 1, fig. 7, pl. 2, figs. 7–8), is distinguished by having a deep lateral glabellar furrow S2, proportionately larger palpebral lobes, and six axial rings on the pygidium.

Onychopyge assula Shergold, Reference Shergold1975, from the lower Tremadocian (Cordylodus proavus Zone) of Australia (Shergold, Reference Shergold1975, pl. 46, figs. 3–4), was erected on the basis of fragments of one cranidium and one pygidium, which seem to differ from O. acenolazai by having a well developed lateral glabellar furrow S2, and a more prominent post-axial ridge.

Onychopyge gonzalezae new species

Figure 13.14–13.20

Diagnosis

Member of Onychopyge with a convex, short (sag.) frontal area; brim furrow concurrent with preglabellar furrow; pygidial axis very long (sag.) and narrow (tr.), composed of seven rings and an elongate terminal piece; posterior pygidial pleural furrows distinct.

Description

Cranidium moderately convex, subtrapezoidal in dorsal view, broadly rounded anteriorly; glabella large, subrectangular in outline, longer than wide, slightly elevated above genal area, delimited by sinuous axial furrows; it occupies ∽85% of the total length of the cranidium; lateral glabellar furrow S1 represented by a rounded pit-like depression close to the axial furrow; S2 and S3 indistinct; occipital furrow slightly curved backward; occipital ring somewhat wider (tr.) than the rest of the glabella, broadly rounded posteriorly, occupying ∽15% of the total glabellar length (sag.); frontal area short (sag.), convex, of uniform length, delimited posteriorly by a transverse, shallow but distinct brim furrow which is concurrent with the preglabellar furrow; anterior facial suture divergent; palpebral lobes large, semicircular, ∽50% length of glabella (sag.), lacking a well defined palpebral furrow. Largest observed cranidium 11 mm long (sag.).

Librigenae, hypostome and thorax unknown.

Pygidium subparabolic in ouline, wider than long, with rounded corners at intersection of anterior and lateral margins, obtusely pointed posteriorly; axis very long, convex, elevated above pleural fields, slightly tapered backward, anterior width 22% maximum width of pygidium, surrounded by narrow axial furrows; it occupies ∽70% of the total pygidial length and is composed of a short (sag.) articulating half-ring, seven axial rings and a long triangular terminal piece; transaxial furrows deep, transverse; pleural fields flat or weakly convex; anterior pleural furrow clearly marked, wide and sinuous, directed posterolaterally, extended into pair of long marginal spines; posterior three pleural furrows distinctive, straight, directed posterolaterally; a delicate postaxial ridge extends from the axis to the posterior pygidial margin; doublure wide, carrying openly spaced terrace lines following the doublural contour. Largest observed pygidium 11.5 mm long (sag.).

Etymology

The species is named for Analía González (Director of School 4424, Salta Province), who offered her hospitality during field work.

Types

Holotype, pygidium, MLP 35147 (Fig. 13.16), length 8.4 mm; paratypes, three cranidia and eight pygidia (MLP 35046, 35049a, 35064, 35065, 35079, 35112, 35124, 35135, 35140a, 35143, 35400).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Although the material described above accords with many of the diagnostic features of Onychopyge Harrington, Reference Harrington1938 (see diagnosis in Harrington and Leanza, Reference Harrington and Leanza1957; Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968; Jell, Reference Jell1985), it differs from most species of this genus by its slightly convex frontal area and its long pygidial axis composed of seven rings and a very elongate (sag.) terminal piece. The type species, O. riojana, from the upper Furongian of La Rioja, Argentina (Harrington, Reference Harrington1938, pl. 5, fig. 30; Harrington and Leanza, Reference Harrington and Leanza1957, figs. 95, 96.2a–c; Tortello and Esteban, Reference Tortello and Esteban2007, figs. 7.5–7.14), shows a proportionately long pygidial axis, distinct posterior pleural furrows, and an obtusely pointed posterior pygidial margin (see especially Tortello and Esteban, Reference Tortello and Esteban2007, fig. 7.5); however, it differs from O. gonzalezae n. sp. in having a concave frontal area lacking an anterior brim furrow. Onychopyge sp. aff. O. riojana, from the Tremadocian of New Zealand (Wright et al., Reference Wright, Cooper and Simes1994, fig. 15B–G), is distinguished, in addition, by its much smaller palpebral lobes.

Onychopyge argentina from the upper Furongian of Jujuy (Harrington and Leanza, Reference Harrington and Leanza1957, fig. 96.1a–d), as well as O. acenolazai from the lower Tremadocian of the Pantipampa section (Fig. 13.1–13.13), are distinguished from O. gonzalezae mainly by their shorter (sag.) pygidial axes, less distinct posterior pleural furrows, and less angular posterior pygidial margin. In addition, the cranidium of O. acenolazai has a laterally expanded frontal glabellar lobe, and a more posteriorly located brim furrow.

Onychopyge harringtoni, from the upper Furongian of the western Cordillera Oriental (Benedetto, Reference Benedetto1977, pl. 2, figs. 14, 15, text-fig. 10), differs from O. gonzalezae in having a concave frontal area, a tapered glabella, and more developed lateral glabellar furrows. As in O. gonzalezae, O. parkerae, from the Tremadocian of Australia (Jell, Reference Jell1985, pl. 23, figs. 1–16, pl. 24, figs. 1–4), exhibits a brim furrow which is concurrent with the preglabellar furrow; however, the Australian species is clearly distinguished by its shorter pygidial axis. Other species of Onychopyge having a relatively short pygidial axis and a concave frontal area (O. sculptura Robison and Pantoja-Alor, Reference Robison and Pantoja-Alor1968; O. assula Shergold, Reference Shergold1975; O. depressa Qian, Reference Qian1986; O. austrina Peng, Reference Peng1984) are also easily differentiated from O. gonzalezae.

Ceratopygidae gen. indet. sp. indet.

Figure 13.21–13.27

Description

Cranidium subtrapezoidal in outline, approximately as long as wide, with pointed anterior margin; glabella elongate, smooth, fairly elevated above genal region, subparallel sided, subtruncate anteriorly, occupying ∽75%–79% of the total cranidial length; median glabellar node delicate, located close to the occipital ring; occipital furrow slightly bowed backward, indistinguishable laterally; anterior cranidial border faintly convex, subequal in length (sag.) to a little shorter or longer than preglabellar field, delimited by a shallow, slightly curved forward border furrow having row of tiny pits; anterior facial suture somewhat divergent; palpebral area of fixigena narrow (tr.); palpebral lobe approximately one-fifth length of cranidium, slightly elevated above fixigena, located at level of glabellar midpoint; posterior fixigena having shallow posterior border furrow and relatively narrow (exsag.) posterior border. Largest observed cranidium 8.2 mm long (sag.).

Pygidium semiellitical in outline, somewhat convex, width approximately twice length, posterior margin entire; axis elevated above level of pleural fields, surrounded by deep and narrow axial furrows, evenly tapering backward, with slightly marked anterior three rings, rounded at posterior end, extending to posterior border; length of axis ∽78%–80% of that of pygidium on sagittal line; pleural field slightly convex, with faint indications of two pairs of oblique pleural furrows; border furrow weak, differentiated by change in slope of exoskeleton; border wide, fairly concave, becoming a little wider posterolaterally; posteromedian margin having a slender indentation. Largest observed pygidium 7 mm long (sag.).

Materials

Seven cranidia and eight pygidia (MLP 4961a, 35033b, 35049b, 35127b, 35128, 35148, 35174–35177, 35181, 35192, 35318a, 35319b, 35321a) from the Pantipampa and Rodeo Colorado sections, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian (Kainella teiichii Zone).

Remarks

The material examined compares with Pseudohysterolenus Harrington and Leanza (Reference Harrington and Leanza1957, p. 191), from the lower Tremadocian of northwestern Argentina, in having a parallel-sided, anteriorly subtruncate glabella, eyes close to glabella, a semielliptical pygidium with a tapered, segmented axis, and a wide pygidial border lacking marginal spines. However, Pseudohysterolenus differs mainly by having indications of lateral glabellar furrows, and a less differentiated anterior cranidial border.

Charchaqia Troedsson, Reference Troedsson1937 (=Aplotaspis Henderson, Reference Henderson1976; Bao and Jago, Reference Bao and Jago2000), from the uppermost Cambrian of North America, China, Australia, and Tasmania (e.g., Troedsson, Reference Troedsson1937; Taylor, Reference Taylor1976; Jago, Reference Jago1991; Bao and Jago, Reference Bao and Jago2000), is similar to the material described above in having an isopygous exoskeleton with low relief, a long and parallel sided glabella without lateral furrows, a tapered pygidial axis, and slight indications of two or three pygidial pleural furrows. Some species show, in addition, a proportionately wide, concave pygidial border. However, Charchaqia is differentiated by its anteriorly placed palpebral lobes. The present material represents a new ceratopygid which is provisionally left under open nomenclature.

Superfamily Trinucleoidea Swinnerton, Reference Swinnerton1915

Family Hapalopleuridae Harrington and Leanza, Reference Harrington and Leanza1957

Genus Hapalopleura Harrington and Leanza, Reference Harrington and Leanza1957

Type species

Hapalopleura clavata Harrington and Leanza, Reference Harrington and Leanza1957, from the lower Tremadocian of the Cordillera Oriental, Argentina, by original designation.

Hapalopleura sp. indet.

Figure 13.28

Materials

Two incomplete cranidia and one fragmentary thorax (MLP 35030a, 35103, 35111) from the Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Despite the efforts made to increase the number of specimens of this taxon, only two imperfect cranidia and one fragmentary thorax were collected from the middle part of the Pantipampa section. They are characterized by having a forwardly expanded and truncate glabella; a wide (sag.) preglabellar field; a downsloping anterior border showing three distinct terrace lines subparallel to margin; and long (tr.) and narrow (exsag.) ocular ridges normal to axis. Therefore, these specimens are assigned to Hapalopleura; a genus (type species: H. clavata Harrington and Leanza, Reference Harrington and Leanza1957) originally described from the lower Tremadocian of the Cordillera Oriental, in association with Kainella, Leptoplastides, Pseudokainella, and Apatokephalus, among others (Harrington and Leanza, Reference Harrington and Leanza1957). The material examined herein is restricted to two levels of the Kainella teiichii Zone (Fig. 2).

Superfamily Cyclopygoidea Raymond, Reference Raymond1925

Family Nileidae Angelin, Reference Angelin1854

Genus Nileus Dalman, Reference Dalman1827

Type species

Asaphus (Nileus) armadillo Dalman, Reference Dalman1827, from the Floian Holen Limestone beds in Östergötland, Sweden, by original designation.

Remarks

Nielsen (Reference Nielsen1995) fully revised the diagnosis of the widespread genus Nileus Dalman and described several representative Baltoscandian species, which are mostly Middle Ordovician in age. The early Tremadocian taxa described below are two of the oldest species of the genus.

Nileus cingolanii new species

Figure 14.1–14.11, 14.14

Figure 14 Nileus from the Santa Rosita Formation in the Iruya area, northwestern Argentina. (1–11, 14) Nileus cingolanii n. sp.: (1) cephalon, MLP 35050a, ×4; (2) cephalon, MLP 35172, ×4.2; (3) cranidium, MLP 35171, ×4; (4) cephalon, MLP 35173, ×4.2; (5) cranidium (holotype) MLP 35036b, ×4.2; (6) cranidium, MLP 35101a, ×4.2; (7) cranidium, MLP 35100, ×4.2; (8) cranidium, latex cast, MLP 35102, ×4.2; (9) pygidium, MLP 35074a, ×4.2; (10) pygidium, MLP 35052, ×4.2; (11) pygidium, MLP 35120a, ×4.2; (14) pygidium, MLP 35056b, ×4.2. (12, 13, 15–21) Nileus erici n. sp.: (12) cranidium, MLP 35084a, ×4.2; (13) cranidium, MLP 35095, ×4.2; (15) pygidium, MLP 35170, ×4.2; (16) fragmentary pygidium, MLP 35062c, ×4.2; (17) cranidium (holotype) MLP 35033a, ×4.2; (18) pygidium, MLP 35084b, ×4.2; (19) pygidium, MLP 35145, ×4.2; (20) pygidium, MLP 35121, ×4.2; (21) pygidium, latex cast, MLP 35120b, ×4.2. All specimens from Pantipampa.

Diagnosis

A Nileus species with a glabella clearly constricted (tr.) at level of palpebral areas; palpebral lobes comparatively large, with their posterior corners located far from glabella; palpebral furrows extremely faint; librigenae having acute genal angles; pygidial axis clearly tapered at anterior half and slightly tapered or nearly parallel sided at posterior half, with four rings and a blunt terminal piece; pygidial border undifferentiated; doublure covered with 14–16 terrace lines.

Description

External surface of exoskeleton without ornamentation; cephalon parabolic in outline, quite convex (sag., tr.), with broadly rounded anterior cranidial margin; cranidium wider than long, with maximum width between the palpebral lobes; glabella very broad, gently arched (sag., tr.), longer than wide, unfurrowed, delimited by faint but perceptible axial furrows, clearly constricted at level of palpebral areas and slightly expanded in front of eyes at a low angle to sagittal line; median glabellar node delicate, situated opposite posterior third of palpebral lobe; occipital brim extremely narrow (sag.), defined by a faint, transverse band furrow; the lateral extremities of the occipital brim show a tiny pit; palpebral lobes conspicuous, pronouncedly arcuate, gently convex, slightly behind of glabellar midpoint, occupying ∽40% of the total length of the cranidium, delimited by extremely faint palpebral furrows, with their posterior corners located far from glabella; posterior branches of facial suture arched, running obliquely backward-outward from posterior corners of palpebral lobes; posterior fixigena triangular, proportionately large, bent slightly down, representing 18% of the total cranidial length; librigena lacking posterior border; genal angle acute, spineless; cephalic doublure possessing at least 12 terrace lines. Largest observed cranidium 8.4 mm long (sag.).

Hypostome and thorax unknown.

Pygidium semielliptical in outline, approximately twice as wide as long, somewhat convex, with well-developed articulating half-ring, rounded anterolateral corners and entire posterior margin; axis little elevated above level of pleural fields, clearly tapered at anterior half and slightly tapered or nearly parallel sided at posterior half, ∽28%–30% of total width of pygidium at anterior extremity; it is composed of four rings, of which only the first two pass completely across the axis, and a blunt terminal piece; length of axis ∽70% of that of pygidium on sagittal line; pleural fields smooth, slightly convex; border undifferentiated; doublure very broad, covered with 14–16 terrace ridges following the doublural contour. Largest observed pygidium 5.5 mm long (sag.).

Etymology

Dedicated to Dr Carlos Cingolani (Museo de La Plata).

Types

Holotype, cranidium, MLP 35036b (Fig. 14.5), length 5.9 mm; paratypes, three cephala, eleven cranidia, one librigena, eight pygidia (MLP 35034a, 35050a, 35051a,b, 35052, 35056b, 35073b, 35074a, 35077, 35100, 35101a, 35102, 35110, 35120a, 35127a, 35132, 35153a, 35168, 35171–35173).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Nielsen (Reference Nielsen1995) pointed out that the outline of the central part of the glabella of Nileus is a useful taxonomic character at specific level. Certainly, the presence of a glabella constricted (tr.) in the middle is one of the most diagnostic features of N. cingolanii n. sp. The type species N. armadillo (Dalman, Reference Dalman1827) (Nielsen, Reference Nielsen1995, figs. 147.A–N, 148.A–O, 149.A–M, 150.A–N; Hansen, Reference Hansen2009, pl. 16, figs. 14–18, pl. 17, figs. 1–11, text-fig. 54) differs from N. cingolanii mainly by having almost straight cephalic axial furrows and, in addition, rounded genal angles, a concave pygidial border of variable width, and an increased number of doublural terrace lines.

Nileus australis Tortello and Esteban, Reference Tortello and Esteban2014, from the upper Tremadocian of the Nazareno area, Cordillera Oriental (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 8.7, 8.13–8.20), is characterized by having a non-constricted glabella, proportionately small palpebral lobes, and a short pygidial axis, and therefore it is easily distinguished from N. cingolanii. Additionally, Nileus porosus Fortey, Reference Fortey1975, from the Valhallfonna Formation of Spitsbergen (Fortey, Reference Fortey1975, pl. 12, figs. 1–14), exhibits well developed terrace lines on the dorsal surface of the pygidium.

Nileus limbatus Brøgger, Reference Brøgger1882, from the upper Tremadocian (Megistaspis armata and lower Megistaspis planilimbata zones) of Norway and Sweden (e.g., Ebbestad, Reference Ebbestad1999, figs. 63.A–O, 64.A–G), differs from N. cingolanii mainly by showing a parallel-sided glabella between palpebral lobes, and a slightly shorter (sag.) pygidial axis. Nileus orbiculatus Tjernvik, Reference Tjernvik1956, from the Floian of Sweden (Tjernvik, Reference Tjernvik1956, pl. 11, figs. 22, 23), is readily distinguished by its medially widened (tr.) glabella.

The absence of a concave, fairly wide pygidial border differentiates N. cingolanii from a large group of species of the genus (e.g., N. exarmatus Tjernvik, Reference Tjernvik1956; N. orbiculatoides Schrank, Reference Schrank1972; N. depressus [Boeck, Reference Boeck1838]).

Nileus erici new species

Figure 14.12, 14.13, 14.15–14.21

Diagnosis

Member of Nileus with a glabella subparallel sided on its posterior two thirds, tapering forward just in front of eyes, and expanding laterally toward the anterior margin; palpebral area of the fixigena relatively narrow (tr.), separated from the glabella by slightly sinuous axial furrow; palpebral furrows faint but distinct; posterior fixigena slender, pointed, and triangular; pygidial axis vaguely perceptible on testaceous material and more evident on internal molds, tapered uniformly, with traces of three rings and a rounded terminal piece; border extremely narrow; doublure covered with 14 terrace lines.

Description

Cranidium slightly wider than long, with maximum width between the palpebral lobes, rather straight anteriorly; glabella subrectangular, gently convex (sag., tr.), longer than wide, subparallel sided on its posterior two thirds, tapering forward just in front of eyes, and expanding laterally toward the anterior margin; median glabellar node almost imperceptible, situated opposite posterior part of palpebral lobes; occipital brim extremely narrow (sag.), showing a pair of lateral pits and a shallow, transverse band furrow; palpebral area of the fixigena relatively narrow (tr.), occupying ∽34%–38% of the maximum cranidial width, separated from the glabella by delicate, slightly sinuous axial furrows; palpebral lobes arcuate, gently convex, slightly behind of glabellar midpoint, occupying ∽44% of the total length of the cranidium, delimited by faint but distinct palpebral furrows; posterior branches of facial suture short, strongly divergent backward; posterior fixigena minute, pointed triangular, downsloping. Largest observed cranidium 8.5 mm long (sag.).

Librigenae, hypostome and thorax unknown.

Pygidium semielliptical in outline, approximately twice as wide as long, somewhat convex, with short (sag.) articulating half-ring, rounded anterolateral corners and entire posterior margin; test surface smooth; axis vaguely perceptible on testaceous material and more evident on internal molds, tapered uniformly, rounded at posterior end, slightly elevated above level of pleural fields, occupying approximately two-thirds of the total length (sag.) of the pygidium, with traces of three rings and a rounded terminal piece; pleural field smooth, slightly downsloping; border extremely narrow, imperfectly indicated by a change of slope of the exoskeleton; doublure very broad, with its anterior margin curved forward, covered with 14 terrace ridges following the doublural contour. Largest observed pygidium 6.8 mm long (sag.).

Etymology

The species is named for Eric Gómez Hasselroth, who has assisted in collecting the specimens studied in this paper.

Types

Holotype, cranidium, MLP 35033a (Fig. 14.17), length 7.8 mm; paratypes, seven cranidia and ten pygidia (MLP 35062c, 35075a, 35084a,b, 35092b, 35095, 35106, 35120b, 35121, 35140b, 35145, 35156b, 35170, 35190, 35194b,c, 35266).

Occurrence

Pantipampa section, Iruya area, northwestern Argentina, Santa Rosita Formation, lower Tremadocian, Kainella teiichii Zone.

Remarks

Nileus erici n. sp. is primarily distinguished from the associated N. cingolanii (Fig. 14.1–14.11, 14.14) in the almost straight cephalic axial furrows, narrower (tr.) palpebral area of the fixigena, more distinct palpebral furrows, smaller posterior fixigena, wider (tr.) pygidial axis, and smaller number of pygidial axial rings.

Nileus erici is comparable with Nileus australis, from the upper Tremadocian of the Nazareno area, Cordillera Oriental (Tortello and Esteban, Reference Tortello and Esteban2014, fig. 8.7, 8.13–8.20), in the general outline of the glabella and the configuration of the pygidium, but the species from Nazareno can be differentiated by the smaller (exsag.) palpebral lobes.

Nileus limbatus, from the upper Tremadocian (Megistaspis armata and lower Megistaspis planilimbata zones) of Norway and Sweden (e.g., Ebbestad, Reference Ebbestad1999, figs. 63.A–O, 64.A–G), differs from N. erici in having a broadly rounded anterior cephalic margin, an almost transverse posterior rachial termination, and an apparent pygidial border. Nileus porosus, from the Valhallfonna Formation of Spitsbergen (Fortey, Reference Fortey1975, pl. 12, figs. 1–14), is distinguished mainly by its more anteriorly placed palpebral lobes.

Nileus latifrons Nielsen, Reference Nielsen1995, from the Middle Ordovician (upper Megistaspis limbata and Asaphus expansus zones) of Scandinavia (Nielsen, Reference Nielsen1995, figs. 152–160), differs from N. erici by having gently arcuate cephalic axial furrows and a variably developed pygidial border. The cranidium of the type species, Nileus armadillo (Nielsen, Reference Nielsen1995, figs. 147.A–N, 148.A–O, 149.A–M, 150.A–N; Hansen, Reference Hansen2009, pl. 16, figs. 14–18, pl. 17, figs. 1–11, text-fig. 54) is very like that of N. erici; however, the pygidium of the former exhibits a well developed border and more numerous terrace ridges. The presence of a concave, fairly wide pygidial border is a distinctive feature of many other species of the genus (e.g., N. exarmatus; N. orbiculatoides; N. depressus).