1. Systematic palaeontology

Class Bivalvia Linnaeus, Reference Linnaeus1758

Subclass Eulamellibranchia Pelseneer, Reference Pelseneer1889

Superorder Heterodonta Neumayr, Reference Neumayr1883

Order Veneroida H. & A. Adams, 1856

Superfamily Corbiculoidea J. E. Gray, Reference Gray1847

Family Corbiculidae J. E. Gray, Reference Gray1847

Genus Polymesoda Rafinesque, Reference Rafinesque1820

Subgenus Pseudocyrena Bourguignat, Reference Bourguignat1854

Type species. Cyrena floridana Conrad, Reference Conrad1846, by monotypy, Moore (Reference Moore1969) extant from the northern Caribbean.

Diagnosis. Small to medium-sized shells, rounded to trigonal in shape; well developed periostracum; hinge commonly with strong posterior and anterior lateral teeth, usually serrate. Concentric ornament.

Occurrence. Cosmopolitan, Eocene to Recent.

Remarks. Extant corbiculids occur in large numbers often choking water bodies.

Polymesoda (Pseudocyrena) obovata (J. Sowerby Reference Sowerby1817)

Plate 1, fig. 1

Plate 1 All figures taken with a digital camera (Fuji FinePix S602Z). Scale bars (figs 1–6, 8–10)=10 mm. All specimens, unless stated otherwise are from the Insect Limestone, Bembridge Marls Member: (1) Corbicula obovata (J. Sowerby Reference Sowerby1817), IWCMS.2007.8, Saltmead, Thorness, Isle of Wight; (2) Melanopsis carinata J. de C. Sowerby, Reference Sowerby1826, IWCMS.2005.32, Bembridge Marls Member, Thorness Bay, Isle of Wight; (3) Tarebia acuta (J. Sowerby Reference Sowerby1822b), IWCMS.2007.7, Bembridge Marls Member, Gurnard, Isle of Wight; (4) Potamaclis turritissima (Forbes, Reference Forbes1853), GSM 119911, Bembridge Marls Member, Hamstead Cliff, Isle of Wight; (5) Viviparus angulosus (J. Sowerby Reference Sowerby1817), IWCMS.2007.1, Saltmead, Thorness, Isle of Wight; (6) Viviparus lentus (Solander Reference Solander1766), G.57288, Gurnard, Isle of Wight; (7) ?Acanthinula sp. NHMUK GG.2904, Sticelets, Thorness Bay, Isle of Wight. Specimen height 1.5 mm; (8) Lymnaea (Galba) longiscata (Brongniart Reference Brongniart1810), MIWG.6016, Thorness Bay, Isle of Wight; (9) Lymnaea (Galba) longiscata (Brongniart Reference Brongniart1810), MIWG.4215, Thorness Bay, Isle of Wight; (10) Planorbarius discus (Edwards Reference Edwards1852), MIWG.4535, Saltmead Ledge, Thorness Bay, Isle of Wight; (11) Gyraulus similis (Férussac Reference Férussac1814), IWCMS.2007.15, Saltmead, Thorness Bay, Isle of Wight. Specimen diameter 4 mm; (12) Hippeutis headonensis (Jodot Reference Jodot1942), IWCMS.2007.11, Sticelets, Thorness Bay, Isle of Wight. Specimen diameter 4.5 mm.

1. 1817 Cycas obovata J. Sowerby, vol. 2 p. 140, pl. 192, figs 4, 5–6.

2. 1822 Cyrena obovata (J. Sowerby); de Férussac & Deshayes, pl. 5, figs 2–3.

3. 1854 Cyrena obovata (J. Sowerby); Morris, p. 200.

4. 1872 Cyrena (Corbicula) obovata (J. Sowerby); Sandberger, p. 261 pl. 15 figs 2, a–b.

5. 1877 Cyrena obovata (J. Sowerby); Wood, p. 12, pl. B, figs 3 a–c.

6. 1891 Cyrena obovata (J. Sowerby); Newton, p. 58.

7. 1901 Corbicula obovata (J. Sowerby); Newton, p. 72.

8. 1966 Polymesoda (Pseudocyrena) obovata (J. Sowerby); Glibert & Van de Poel, p. 10.

9. 1971 Corbicula obovata (J. Sowerby); Castell, pl. 11, fig. 1.

Syntypes. NHMUK 43092, Sowerby Collection, Two specimens. However, a third specimen included under the same number excluded from the type series is re-identified herein as Polymesoda convexa (Brongniart Reference Brongniart1810) from the Woolwich Beds (=Woolwich Formation).

Type locality and horizon. Barton Cliff, ‘Barton Clay’.

Referred material. IWCMS.2007.8, from Saltmead, Thorness, Isle of Wight, single right valve.

Diagnosis. Small, equivalved, equilateral, rounded-trigonal in shape. Prominent umbones, height approximately equals length. Posterior margin truncated. Corbiculoid dentition, long serrate laterals.

Distribution. Headon Hill Formation, Bembridge Limestone Formation and Bembridge Marls Member of the Solent Group (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and southwest Hampshire, southern England.

Description. The shell is small and thick, equivalved, equilateral, prosocline, rounded- trigonal in outline shape, inflated. Height, up to 18mm, approximately equals the length. Prominent umbones located towards the anterior of the shell, prosgyrate. The posterior margin, which is truncated/angular to the umbones and ventral margin, is shallowly convex. The ventral margin is shallowly convex, antero-ventral margin convex, antero-dorsal margin concave. The flanks have numerous moderate to strong, regularly spaced growth bands.

The interior of the shell is smooth, the umbonal cavity deep. The pallial line is complete, with a shallow pallial sinus anterior of the posterior abductor muscle. The anterior abductor muscle is large, shallow and oval in shape. The posterior abductor muscle is shallow, large and triangular in shape. The dentition is typically corbiculoid with the formula:

AI AIII 3a 1 3b PI PIII

AII 2a 2b 4b PII

The laterals are serrate, with the anterior laterals approximately half the length of the posterior laterals.

Remarks. This is the most abundant bivalve in the lower part of the Bembridge Marls Member. It occurs as paired, but more frequently disarticulated, valves and rounded fragments. The shells are usually etched. The specimens from the Insect Limestone comprise a single corroded and etched valve and numerous rounded fragments in a single block.

Class Gastropoda Cuvier, Reference Cuvier1797

Infraclass Apogastropoda Salvini-Pläwen & Haszprunar, Reference Salvini-Pläwen and Haszprunar1987

Superorder Caenogastropoda Cox, Reference Cox1960

Order Sorbeoconcha Ponder & Lindberg, Reference Ponder and Lindberg1997

Superfamily Cerithioidea Férussac, Reference Férussac and Deshayes1819

Family Thiaridae Troschel, Reference Troschel1857

Genus Tarebia H. & A. Adams, 1854

Type species. Melania granifera Lamarck, Reference Lamarck1822, by subsequent designation by Brot (Reference Brot, Küster, Martini and Chemnitz1874), natural distribution Southeast Asia, southern China.

Diagnosis. Small to medium-sized, turreted, strong axial ribs, which in later growth become dissolved into two or three spiral rows of tubercles, the axial ornament is replaced by strong spiral ribs at the base of the last whorl.

Occurrence. Southeast Asia, introduced into the Caribbean, southern USA and South Africa, extant.

Remarks. Following Brandt (Reference Brandt1974) and Glaubrecht (Reference Glaubrecht1996) Tarebia is treated herein as a genus and not a subgenus of Melanoides Olivier, Reference Olivier1804. However, Genner et al. (Reference Genner, Todd, Michel, Erpenbeck, Jimoh, Joyce, Piechocki and Pointier2007), based upon mitochondrial DNA sequences of extant thiarids including Melanoides species and Tarebia granifera, have concluded that Tarebia falls within Melanoides and may not be a discrete genus. Moreover, that specimens assigned to Tarebia older than Early Pliocene age cannot be unequivocally identified as such, and that Tarebia in the Priabonian (and Early Oligocene) requires systematic revision. It is not within the capacity of this work to undertake such a revision. Therefore existing taxonomy is retained herein.

Tarebia acuta (J. Sowerby Reference Sowerby1822b)

Plate 1, fig. 3

1. 1822b Potamides acutus J. Sowerby, vol. 3, p. 53, pl. 341, fig. 2.

2. 1856 Melania muricata Morris; Forbes, p. 151, pl. iii, fig. 16.

3. 1856 Melania muricata var. costata Morris; Forbes, p. 148, pl. ii, fig. 14.

4. 1889 Melania (Tarebia) acuta (J. Sowerby); Vincent, p. cxxix.

5. 1891 Melania acuta (J. Sowerby); Newton, p. 200.

6. 1909 Tarebia muricata S. Wood; Cossmann, p. 134.

7. 1954 Melania (Tarebia) acuta (J. Sowerby); Glibert & Heinzelin, p. 352, pl. v, figs.16a, b.

8. 1958 Tarebia acuta (J. Sowerby); Castell, pl. 19, figs. 3 & 4.

9. 1975 Melanoides (Tarebia) acuta (J. Sowerby); Castell, pl. 19, fig. 2.

Syntype. BMGD. 43558. Sowerby Collection, Natural History Museum, London.

Type locality and horizon. ‘Lower Freshwater Formation’ (=Solent Group), Isle of Wight.

Referred material. IWCMS.2007.7 Saltmead, Thorness, Isle of Wight; IWCMS.2003.41 Saltmead, Thorness, Isle of Wight; IWCMS.2007.20 all from Saltmead, Thorness, Isle of Wight; NHMUK G. 24642 Gurnard, Isle of Wight.

Diagnosis. Small, up to 14 mm in height, turreted to turreted-conical, whorls shallowly convex. Suture strong, canaliculate. The ornament is cancellate and variable, comprising up to three lines of linked pustules or spines, strong axial costae. Last whorl comprises half of shell height. Aperture is large and oval.

Distribution. Solent Group (excluding Cranmore Member) (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and southwest Hampshire, southern England.

Description. (Table 1) Small in size, up to 14 mm in height; width at the last whorl up to 5.5 mm. Turreted to turreted-conical in shape. Teleoconch of up to seven flat to shallowly convex whorls. The suture is strong, canaliculate. The strength of the suture and rate of whorl expansion gives the shell a stepped profile. The last whorl comprises one half of the total shell height. The protoconch is variable.

Table 1 Tarebia acuta biometric data

¹ Specimens from bulk samples.

The aperture is large and oval. The inductura is smooth and narrow, its leading edge forming a continuous arc from the adapical margin to the base of the aperture. The inner surface of the outer lip is ornamented correspondingly with the main external ornament. The shell is moderately thick. The siphonal canal is very weak, broad and shallow.

The growth lines are very shallowly opisthocyrt, almost orthocline and closely spaced. They vary in strength from faint to very strong and weakly laminar. The ornament is cancellate, which in the early whorls comprises two, becoming three or five in later whorls, lines of linked spiral pustules, tubercles or spines; these are linked by axial costae and varices are formed. Where there are two lines of protruberances they comprise a and d. When there are three lines, they are a, c and d. Where there are five spiral lines, d and e are very closely set, with a, c and d being stronger than b and e. The base of the last whorl carries up to six strong spiral bands.

Remarks. This taxon is highly variable in shape and ornamentation; Morris (Reference Morris and Forbes1856) recognised two varieties (which, under ICZN rules, are now regarded as subspecies), specimens from the Insect Limestone belong to T. acuta sensu stricto.

Family Melanopsidae H. & A. Adams, 1854

Genus Melanopsis Férussac, Reference Férussac1807

Synonymy. Nana Schumacher, Reference Schumacher1817 Melanithes Swainson, Reference Swainson1840 Canthidomus Swainson, Reference Swainson1840 Lyrcaea H. & A. Adams, 1854

Type species. Buccinum costata Gray, Reference Gray1847 (synonym of Buccinum praemorsus Linné, 1758 by original designated from southern Spain and North Africa).

Diagnosis. Subulate to turreted, thin shelled, smooth or ornamented with striations, aperture pyriform or oval, callus smooth.

Melanopsis carinata J. de C. Sowerby, Reference Sowerby1826

Plate 1, fig. 2

1. 1826 Melanopsis carinata Sowerby, J. de C., vol. 6, p. 41, pl. 523, fig. 1.

2. 1856 Melanopsis carinata Sowerby, J. de C.; Forbes, p. 156, pl. vi, figs 8 & 9.

3. 1873 Macrospira carinata (Sowerby, J. de C.); Sandberger, pp. 248, 314; pl. 14, fig. 19; pl. 20, fig. 10.

4. 1891 Melanopsis carinata Sowerby, J. de C.; Newton, p. 202.

5. 1889 Melanopsis carinata Sowerby, J. de C.; Bristow et al., p. 292, fig. 66.

6. 1929 Melanopsis carinata carinata Sowerby, J. de C.; Wenz, p. 2686.

7. 1962 Melanopsis (Stylospirula) carinata (Sowerby, J. de C.); Glibert, p. 146.

Syntype. BMGD 43548. Sowerby Collection, Natural History Museum, London. Locality not recorded. The specimen appears to have been removed from its original small block as illustrated by Sowerby (Reference Sowerby1826, pl. 523 fig. 1).

Referred material. IWCMS.2007.9 Saltmead, Thorness, Isle of Wight.

Diagnosis. Small sized up to 17 mm, fusiform, slender, aperture pyriform; distinctive carina is formed along the suture.

Distribution. Barton Group to Solent Group (excluding Cranmore Member) (Bartonian, Middle Eocene to Rupelian, Early Oligocene) Isle of Wight, southwest Hampshire and southeast Dorset.

Description. (Table 2) Small in size, up to 17mm in height; width at last whorl up to 8mm. Fusiform in shape, with mean apical angle of 29°. Teleoconch of up to eight whorls. The early whorls may be either concave or shallowly convex. The last whorl, which forms two-thirds of the total shell height, appears to be shallowly convex, but in apertural view is subtly concavo-convex in profile. The adapical and abapical edges of the whorls are markedly flared, forming distinctive carinae along the sutures. The whorls are occasionally imbricate; however, the adapical edge of the whorl may rise above the flare. In the early whorls the suture is faint, becoming strong in the last whorl. The suture often shows ‘V’ and step-like interruptions. The line of the carina/suture may be sinuous. In the last whorl, the concave part of the shell is set above the top of the aperture. The shell is thin.

Table 2 Melanopsis carinata biometric data

The aperture is large and pyriform, becoming slit-like adapically: this slit is closed just behind the outer lip. The inductura is smooth and inflated; it is wide and forms a continuous convex arc from the base of the siphonal canal to the top of the aperture. The siphonal canal is short, deep but narrow, curved slightly towards the front of the shell. The inner surface of the outer lip is smooth.

The growth line is opisthocyrt, sinuous like a laterally flattened ‘S’. The growth line is faint to strong, strong where there is a break in growth indicated, coincident with a step or ‘V’-shaped interruption in the suture.

Remarks. This species is most similar to Melanopsis morrisi Wenz, Reference Wenz1928 which is also found within the Solent Group. However, the shell of M. carinata is more slender/fusiform and a shoulder is not formed. Melanopsis carinata is often very abundant and occurs with freshwater taxa such as Viviparus lentus. Melanopsis carinata is the most common melanopsid in the lower part of the Bembridge Marls Member.

Superfamily Rissooidea Gray, Reference Gray1847

Family Hydrobiidae Troschel, Reference Troschel1857

Subfamily Amnicolinae Tryon, Reference Tryon1863

Genus Potamaclis Sandberger, Reference Sandberger1873

Type species. Melania turritissima Forbes, Reference Forbes1853, by subsequent designation by Clessin (Reference Clessin1880), Oligocene (=Solent Group, Late Eocene–Early Oligocene), Hempstead (=Hamstead, Isle of Wight) and Hordwell (=Hordle, Hampshire), southern England.

Diagnosis. Small sized high-spired, turreted shells with convex whorls.

Occurrence. Europe, Eocene-Pliocene.

Potamaclis turritissima (Forbes Reference Forbes1853)

Plate 1, fig. 4

1. 1853 Melania turritissima Forbes, p. 266.

2. 1856 Melania turritissima Forbes; Morris in Forbes, p. 150, pl. 3, fig. 14.

3. 1873 Potamaclis turritissima (Forbes); Sandberger, p. 312, pl. 10, figs 5–5c.

4. 1891 Potamaclis turritissima (Forbes); Newton, p. 234.

5. 1901 Potamaclis turritissima (Forbes); Newton, p. 67.

6. 1921 Hydrobia (Potamaclis) turritissima (Forbes); Cossmann, p. 111, pl. 3, figs 79–80.

7. 1929 Potamaclis turritissima (Forbes); Wenz, p. 2630.

8. 1962 Potamaclis turritissima (Forbes); Glibert, p. 32.

9. 1975 Potamaclis turritissima (Forbes); Castell, pl. 19, fig. 9.

Holotype. GSM 119911, Forbes Collection, British Geological Survey Museum.

Type locality and horizon. ‘Bembridge Series’ (=Bembridge Marls Member), Hamstead Cliff, Isle of Wight.

Referred material. IWCMS.2007.18, Thorness Bay, Isle of Wight.

Diagnosis. Small, needle-like shell comprising 12 or 13 whorls, slightly asymmetrical convex whorls with strongly adpressed suture.

Distribution. Headon Hill Formation, Bembridge Marls Member and Hamstead Member (Bouldnor Formation) of the Solent Group (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and Hampshire, southern England.

Description. (Table 3) Small, up to 14 mm in height, width of last whorl up to 3 mm. Needle-like turreted in shape, teleoconch typically of 12–13 whorls. The whorls which are slightly asymmetrical are moderately convex. The suture is strong, adpressed. There is a slight overlap of the top of the whorl over the base of the previous whorl. The last whorl comprises approximately one third of the total shell height. The protoconch comprises one and a half whorls, which are smooth and expand rapidly.

Table 3 Potamaclis turritissima biometric data

The aperture is large, oval to slightly pyriform. The inductura is narrow, smooth and irregular in outline. The peristome is holostomatous. The shell is thick, the inner lip is smooth. The growth line is moderate to strongly opisthocyrt, the shell is otherwise smooth.

Remarks. This is a very distinctive taxon that occurs in vast numbers along bedding planes, particularly in the Bembridge Marls Member. Based upon shell shape and co-occurrence with molluscs such as Unio, Paul (Reference Paul1989) considered this extinct genus to have lived in fast-flowing freshwater. Specimen IWCMS.2007.18 comprises a current-aligned mass of shells associated with Melanopsis carinata J. de C. Sowerby, Reference Sowerby1826, a frequent association in the Solent Group (pers. obs.).

Order Architaenioglossa Haller, Reference Haller1890

Superfamily Ampullarioidea Gray Reference Gray1824

Family Viviparidae Gray, Reference Gray1847

Subfamily Viviparinae Gray, Reference Gray1847

Genus Viviparus Montfort, Reference Montfort1810

Synonymy. Vivipara J. Sowerby, Reference Sowerby1813. Paludina Lamarck, Reference Lamarck1822.

Type species. Helix vivipara Linnaeus, Reference Linnaeus1758, by original designation, distributed across Europe.

Diagnosis. Turbinate in shape, 20–60 mm in height, with concentrically growing horny operculum, sexual dimorphism with female shells larger and more inflated.

Occurrence. Northern Eurasia, Europe, Asia Minor and North America. Jurassic–Recent.

Viviparus angulosus (J. Sowerby Reference Sowerby1817)

Plate 1, fig. 5

1. 1817 Phasianella orbicularis J. Sowerby, vol. 2, p. 167, pl. 175, fig. 1.

2. 1817 Phasianella angulosa J. Sowerby, vol. 2, p. 168, pl. 175, fig. 2.

3. 1835 Paludina angulosa (J. Sowerby); J. de C. Sowerby, p. 246.

4. 1891 Viviparus angulosus (J. Sowerby); Newton, p. 225.

5. 1975 Viviparus angulosus (J. Sowerby); Castell, pl. 17, fig. 13.

Syntype. BMGD. 43563. Sowerby Collection, Natural History Museum, London (two specimens).

Type locality and horizon. Shalcombe, Isle of Wight, Bembridge Limestone Formation (Solent Group).

Referred material. IWCMS.2007.1, Saltmead, Isle of Wight.

Diagnosis. Large, up to 45 mm turbinate, high spired, globose shell. Convex whorls with strong rounded carina at the whorl base, visible in internal moulds. Large rounded aperture.

Distribution. Headon Hill Formation, Bembridge Limestone Formation and Bembridge Marls Member (Bouldnor Formation), Solent Group (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and Hampshire, southern England.

Description. (Table 4) Large, up to 45mm in height; width at the last whorl up to 40mm. Turbinate, high-spired, globose shell shape. Teleoconch of up to five convex whorls. The whorls are asymmetrical being shallowly convex on the apertural side, more convex on the opposite. The suture is strong, impressed, on internal moulds the suture is canaliculate. The last whorl comprises almost three-quarters of the total shell height. On internal moulds there is a strong, but rounded carina visible at the base of the whorl. Where the shell is preserved, this is not so obvious. Protoconch imperfectly known but comprises of at least one and a half convex whorls. Start of teleoconch defined by onset of shallower whorl development.

Table 4 Viviparus angulosus biometric data

¹ Syntypes of Vivipara angulosa, Bembridge Limestone Formation

² Syntype of Vivipara orbicularis, Bembridge Limestone Formation

³ Syntype of Vivipara orbicularis, ‘Headon Beds’

The aperture is large and round. The inductura is narrow and irregular in extent and surface shape. The peristome is holostomatous. The shell is thin.

The growth lines are moderate to strong, prosocline. Attenuation of growth is marked by strong growth line development. The early whorls carry up to seven evenly spaced fine spiral cords. These eventually (by the third whorl?) become obscured by closely spaced growth lines.

Remarks. This species is found almost exclusively in limestones in the Solent Group and is particularly abundant in the Bembridge Limestone Formation. It is substantially larger than Viviparus lentus (Solander Reference Solander1766), which is found within clastic sediments in the Solent Group. Paul (Reference Paul1989) used the extant Pomacea spp. which occupies well weeded pools in the Florida Everglades as an analogue for V. angulosus. The extant British species V. viviparus and V. fasciatus are both found in hard water areas (Macan Reference Macan1977); the latter is known to occupy stagnant water. Viviparus angulous is known from a single specimen from the Insect Limestone at Thorness. This specimen is extremely useful, as examples from the Bembridge Limestone Formation are usually internal moulds, or the shell is more or less coarsely re-crystallised calcite, which obscures surface details.

Viviparus lentus (Solander Reference Solander1766)

Plate 1, fig. 6

1. 1766 Helix lenta Solander, p. 29; pl. iv, fig. 60.

2. 1813 Vivipara lenta (Solander); J. Sowerby, vol. 1, p. 79; pl. 31, fig. 3.

3. 1891 Viviparus lentus (Solander); Newton, p. 225.

4. 1975 Viviparus lentus (Solander); Castell, pl. 17, fig. 14.

Holotype. ? NHMUK G.98292 Brander Collection, Natural History Museum, London.

Type locality and horizon. Headon Hill Formation, Hordle, Hampshire.

Referred material. NHMUK G.57288, NHMUK G.57289, Gurnard Bay, Isle of Wight. MIWG.6545, Totland Bay, Isle of Wight.

Diagnosis. Medium-sized, up to 28 mm high, turbinate globose with convex whorls. Suture strong and impressed. Weak spiral ornament largely obscured by strong prosocline growth lines. Aperture large and round.

Distribution. Solent Group (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and southwest Hampshire, southern England.

Description. (Table 5) Medium-sized, up to 28 mm in height, width at last whorl up to 22 mm. Turbinate globose in shape, high-spired with step-like outline. Teleoconch of four moderately convex, shouldered whorls. The suture is strong impressed. The last whorl comprises over two thirds of the total shell height. The protoconch is typically absent.

Table 5 Viviparus lentus biometric data

The aperture is large and round. The inductura is narrow but thick, commonly eroded revealing successive laminae, the leading edge is frequently broken and irregular. However, the inductura is continuous from the base of the aperture to the top of the outer lip. The shell is thick and the inner surface of the shell is smooth. The peristome is holostomatous. The umbilicus, which is mostly obscured, appears to be shallow, with a rounded edge.

The growth lines are fine to strong and densely packed, shallowly prosocline. The shell is ornamented with numerous very fine threads. Otherwise, there are two stronger threads, the upper of which defines the shoulder in the upper one quarter of the whorl and the lower is located along the midline of the whorl, dropping towards the base of the whorl in the last whorl. The shell appears superficially smooth and shiny.

Remarks. Considerably smaller than V. angulosus, Viviparus lentus is abundant in argillaceous sediments within the Solent Group, and is also present in arenaceous units such as the Seagrove Bay Member. Paul (Reference Paul1989) correlated the occurrence of V. lentus with fluvial and lacustrine facies. Viviparus lentus is known from two specimens from the Insect Limestone, collected from Gurnard. The shells appear to be a slightly unusual lithology; however not beyond the range of lithologies seen in the Thorness Bay section.

Subclass Euthyneura Spengel, Reference Spengel1881

Order Pulmonata Cuvier, Reference Cuvier1817

Suborder Stylommatophora A. Schmidt, Reference Schmidt1855

Superfamily Pupilloidea Turton, Reference Turton1831

Family Valloniidae Morse, Reference Morse1864

Subfamily Acanthinulinae Steenberg, Reference Steenberg1917

Genus Acanthinula Beck, Reference Beck1847

Type species. Helix aculeata Müller, Reference Müller1774, by subsequent designated by Albers & Martens (Reference Albers and Marten1860), distributed in northwest and southern Europe.

Diagnosis. Small, conical, with up to four well rounded whorls, aperture round, regularly spaced sharp ribs.

Occurrence. Europe and North America, Eocene to Recent.

Remarks. The extant Acanthinula aculeata (Müller Reference Müller1774) is found in woodland and scrub, occasionally in more open habitats (Kerney & Cameron Reference Kerney and Cameron1979).

?Acanthinula sp.

Plate 1, fig. 7

Material. NHMUK GG. 22904, Sticelets, Thorness Bay, Isle of Wight.

Description. Small, 1.5mm in height and width. Turbinate globose shell shape. Teleoconch of four convex whorls. The suture is strong impressed. The protoconch is unknown. Aperture shape unknown. Growth lines fine opisthocyrt. Numerous fine curved ribs.

Remarks. Resembles Strobilops pseudolabyrinthica (Sandberger Reference Sandberger1873). However, in the specimen from the Insect Limestone, the whorls are slightly more shouldered and convex.

Subordinal Grade Basommatophora Kerferstein, Reference Keferstein and Bronn1864

Superfamily Lymnaeoidea Rafinesque, Reference Rafinesque1815

Family Lymnaeidae Rafinesque, Reference Rafinesque1815

Subfamily Lymnaeinae Rafinesque, Reference Rafinesque1815

Genus Lymnaea Lamarck, Reference Lamarck1799

Subgenus Galba Schrank, Reference Schrank1803

Synonymy. Stagnocola Leach in Jeffreys, Reference Leach and Jeffreys1830 Limnophysa Fitzinger, Reference Fitzinger1833 Omphiscola Beck, Reference Beck1838 non Rafinesque, Reference Rafinesque1819 Leptolimnaea Swainson, Reference Swainson1840

Type species. Buccinum truncatulum Müller, Reference Müller1774, type species by subsequent designated under the plenary powers (ICZN 2001, p. 33), distributed in northwest and southern Europe.

Dignosis. Small to large sized; elongate-oval with convex whorls; aperture narrowly oval; columella straight; umbilicus slit-shaped.

Occurrence. Europe, North America, South America, Asia, Africa. Jurassic–Recent.

Remarks. The type species Lymnaea (Galba) truncatula is extant and widespread in Europe and the Middle East. It is found in rivers and small streams and the edges of ditches (Macan Reference Macan1977).

Lymnaea (Galba) longiscata (Brongniart Reference Brongniart1810)

Plate 1, figs. 8–9

1. 1809 Lymnée effilée Brard, vol. 14, p. 432, pl. 27, figs 15–16.

2. 1810 Limneus longiscatus Brongniart, p. 372, pl. 22, fig. 9.

3. 1822b Limnaea longiscata Brongniart; Sowerby, J., vol. 4, p. 57, pl. 343.

4. 1852 Limnaea longiscata Brongniart; Edwards, p. 85, pl. xii, figs 3a–3b.

5. 1863 Limnaea longiscata Brongniart; Deshayes, vol. 2, p. 722.

6. 1889 Limnaea longiscata Brongniart; Cossmann, fasc. 4, p. 329.

7. 1891 Limnaea longiscata Brongniart; Newton, p. 278.

8. 1913 Limnaea longiscata Brongniart; Cossmann & Pissarro, vol. 2, pl. LVI, fig. 53-1.

9. 1923 Galba (Galba) longiscata longiscata (Brongniart); Wenz, vol. 4, pp 1373–1384.

10. 1975 Galba longiscata (Brongniart); Castell, p. 84, pl. 27, fig. 7.

11. 1989 Stagnicola longiscata (Brongniart); Fischer, p. 348.

Type material. Repository unknown.

Type locality and horizon. Unknown.

Referred material. MIWG.852 and MIWG.4215, Thorness Bay, Isle of Wight; MIWG. 3611, MIWG.6013, MIWG.6016, Gurnard, Isle of Wight; MIWG.4536–MIWG.4538, Saltmead, Isle of Wight; MIWG.4551, Gurnard Point, Isle of Wight; IWCMS.2007.17 Saltmead, Isle of Wight; IWCMS.2007.21, Saltmead, Isle of Wight. NHMUK G.37984–G.37989, NHMUK G.57301–NHMUK G.57304, BMGD.57295–BMGD. 57300, all from Gurnard, Isle of Wight.

Diagnosis. Large, up to 35mm, fusiform with moderately convex whorls, strong, adpressed suture, aperture large and flattened oval shape, thin smooth shell.

Distribution. Solent Group (Priabonian, Late Eocene to Rupelian, Early Oligocene), Isle of Wight and Hampshire, southern England. Bacini Continentali (Eocene–Oligocene) Majorca, Spain. La Calcaire Lacustre de Saint-Ouen (Bartonian), Paris Basin, France.

Description. (Table 6) Large-sized, up to 28 mm in height; width at last whorl up to 12 mm. Fusiform in shape, with an apical angle between 34° and 36° (data based upon specimens from the Insect Limestone). Teleoconch of up to six shallowly convex whorls. The suture is strong adpressed. Sutural angle between 15° and 20°. The last whorl, which is sometimes shouldered, comprises two-thirds of the total shell height. Protoconch comprising one and a half shallow, convex whorls.

Table 6 Lymnaea (Galba) longiscata biometric data

The aperture is large, flattened oval-shaped. The inductura is smooth and narrow, with an irregular/broken adaxial margin. The shell is thin, the inner surface of which is smooth. The peristome is uninterrupted; however, the abapical margin of the peristome is slightly flattened. The columella has a single, broad flat plication, there is a small umbilical slit, usually obscured by the inductura. The growth lines are faint, prosocyrt, the shell is smooth.

Remarks. Wenz (Reference Wenz and Pompeckj1923) provides an extensive synonymy for this taxon. Both Sowerby (Reference Sowerby1822b) and Edwards (Reference Edwards1852) noted that this shell is highly variable in form. Edwards proposed a variety (subspecies) distorta (Edwards Reference Edwards1852, p. 86, pl. 12, figs 3e–h) to accommodate the most extreme variation of the shell with a shorter aperture and higher sutural slope, giving a partly uncoiled, distorted appearance. Due to their morphoanatomic uniformity, the classification of the Lymnaeidae into subgenera is difficult (Bargues & Mas-Coma Reference Bargues and Mas-Coma1997). Lymnaea (Galba) longiscata shows a range of characters seen in the extant subgenera of Lymnaea, namely (L.) Lymnaea, Galba and Radix. The subgenus Stagnicola was synonymised on the basis of 18S rDNA sequences with Lymnaea by Bargues & Mas-Coma (Reference Bargues and Mas-Coma1997). Due to the difficulty in separating the different subgenera, herein Galba is retained, as it is the subgeneric name most frequently used to accommodate this widespread taxon.

Specimens collected from the Insect Limestone generally have their shells preserved and are frequently found in groups that appear to have drifted together. Preservation, which is generally excellent, varies from a white-grey colour to black with pyrite growth. This species is particularly abundant in the Bembridge Limestone Formation and throughout the freshwater parts of the Solent Group. Paul (Reference Paul1989) remarked that the numerous forms of Lymnaea described by Edwards (Reference Edwards1852) are almost certainly shape varieties of the larger species (in the Solent Group); therefore care should be used when identifying lymnaeids from the Solent Group. These nominal taxa require further study before formal synonymisation can be undertaken.

There are some similarities between Lymnaea (Galba) longiscata (Brongniart Reference Brongniart1810) and Palaeoglandina costellata (J. Sowerby Reference Sowerby1822b). The latter is ornamented with fine axial ribs, the suture less pronounced, with the proceeding whorl over – lapping the previous whorl.

Superfamily Planorboidea Rafinesque, Reference Rafinesque1815

Family Planorbidae Rafinesque, Reference Rafinesque1815

Subfamily Planorbinae Rafinesque, Reference Rafinesque1815

Genus Planorbarius Froriep, Reference Froriep and Duméril1806

Synonymy. Planorbina Haldeman, Reference Haldeman1842 (part)

Type species. Helix corneus Linnaeus, Reference Linnaeus1758, by original designation, distribution northwest and southern Europe.

Diagnosis. Planispiral, small to large sized, whorls rounded, aperture subcircular-oval.

Occurrence. Late Eocene to Recent, Europe, North Africa and Asia.

Remarks. Historically, planorbid generic assignment has been influenced by geographical distribution (see summary and discussion by McKenna et al Reference Mckenna, Robinson and Taylor1962), with Planorbarius, Froriep, Reference Froriep and Duméril1806 used for some European forms. Based upon the systematic usage of Zilch (Reference Zilch and Schindewolf1959–60), Paul (Reference Paul1989) used Australorbis Pilsbry, Reference Pilsbry1934 to accommodate the larger planorbids from the Solent Group; however, Paul (Reference Paul1989) noted that Australorbis may be a synonym of Biomphalaria Preston, Reference Preston1910. Herein the generic name Planorbarius is retained; however, there is clearly a case for review.

Planorbarius discus (Edwards Reference Edwards1852)

Plate 1, fig. 10

1. 1852 Planorbis discus Edwards, p. 102; pl. xv, figs 7a–b.

2. 1873 Planorbis discus Edwards; Sandberger, p. 285; pl. xvi, fig. 4 p.

3. 1891 Planorbis discus Edwards; Newton, p. 281.

4. 1923 Planorbina (Planorbina) discus (Edwards); Wenz vol. 5, pp. 482–1484.

5. 1964 Planorbis (Coretus) cf. discus (Edwards); Soyer, p. 145.

6. 1971 Planorbina discus (Edwards); Castell, pl. 27, fig. 4.

7. 1989 Australorbis discus (Edwards); Paul, p. 157.

8. 1995 Planorbarius cf discus (Edwards); Le Renard, p.66608.

Syntypes. NHMUK GG.6933 and NHMUK GG.6934 (ex BMGD.71078), Sconce, Isle of Wight.

Type locality and horizon. Sconce, Isle of Wight, Bembridge Limestone Formation.

Referred material. BMGD.83039 Gurnard Bay, Isle of Wight. MIWG.4535, Saltmead Ledge, Thorness, Isle of Wight.

Diagnosis. Large, up to 37 mm in diameter, planispiral, four whorls, smooth. Adapical side shallowly convex, abapical side concave.

Distribution. Headon Hill Formation, Bembridge Limestone Formation (Solent Group), Bembridge Marls Member and Hamstead Member (Bouldnor Formation, Solent Group), Isle of Wight and Hampshire, southern England.

Description. (Table 7) Large-sized, up to 37 mm in diameter, height up to 10 mm. Planispiral in shape. Teleoconch of up to four convex whorls. The adapical side is shallowly convex, the abapical side concave. The suture is strong, grooved. The whorls expand gradually. Protoconch obscured.

Table 7 Planorbarius discus (Edwards, Reference Edwards1852) biometric data

The whorls are the same shape as the aperture, which is a shallow asymmetrical oval, with the abapical edge of the peristome more convex adaxially. The shell is thin and the inner surface smooth. The peristome is holostomatous. The growth lines are moderately pronounced and prosocyrt.

Remarks. This taxon is common in the limestones of the Solent Group and is the largest planorbid present in the Insect Limestone.

Genus Gyraulus Charpentier, Reference Charpentier1837

Synonymy. Planaria Brown, Reference Brown1827 non Müller, Reference Müller1774. Trochlea Haldeman, Reference Haldeman1841. Nautilina Stein, Reference Stein1850 (part). Giraulus Moquin-Tandon, Reference Moquin-Tandon1855. Gyrulus Gray, Reference Gray1857.

Type species. Planorbis hispidus Draparnaud, Reference Draparnaud1805, by subsequent designated by Wenz (Reference Wenz and Pompeckj1923, p. 1540). Distributed over Europe, northern Asia and North Africa.

Diagnosis. Planispiral, small to large sized, whorls rounded, aperture subcircular-oval.

Occurrence. Jurassic to Recent, Europe, North Africa and Asia.

Gyraulus similis (Férussac, Reference Férussac1814)

Plate 1 fig. 11

1. 1809 Planorbe arrondi Brard, p. 433, pl. 27, figs 19–20.

2. 1810 Planorbis rotundatus Brongniart, p. 370, pl. 22, figs 4–5 non Poiret, Reference Poiret1801.

3. 1814 Planorbis similis Férussac, p. 61.

4. 1847 Planorbis platystoma Wood, p. 118.

5. 1852 Planorbis rotundatus Brongniart; Edwards, p. 100, pl. 15, figs 4a–c.

6. 1852 Planorbis platystoma Wood; Edwards, p. 103, pl. 15, figs 2a–d.

7. 1873 Planorbis (Menetus) goniobasis Sandberger, p. 272, pl. 15, figs 21–21b.

8. 1891 Planorbis goniobasis Sandberger; Newton, p. 282.

9. 1891 Planorbis platystoma Edwards; Newton, p. 283.

10. 1901 Planorbis (Menetus) goniobasis Sandberger; Newton, p. 67.

11. 1901 Planorbis platystoma Edwards; Newton, p. 67.

12. 1923 Planorbina (Planorbina) similis (Férussac); Wenz, p. 1505.

13. 1962 Planorbis similis Férussac; Glibert, p. 85.

Type material. Repository unknown.

Type horizon and locality. Unknown.

Referred material. IWCMS.2007.15, IWCMS.2007.16; both from Saltmead, Thorness Bay, Isle of Wight.

Diagnosis. Large, up to 30 mm, planispiral, convex whorls, aperture oval, adapical surface deeply concave.

Distribution. Headon Hill Formation, Bembridge Limestone Formation (Solent Group), Bembridge Marls Member and Hamstead Member (Bouldnor Formation, Solent Group), Isle of Wight and Hampshire, southern England.

Description. Large-sized, up to 30 mm in diameter, height up to 8 mm. Planispiral in shape. Teleoconch of up to seven convex whorls, the adapical surface of which are flattened. The adapical side is very shallowly convex, the abapical side deeply concave. The suture is strong, grooved. The whorls expand gradually. Protoconch obscured.

The aperture is oval in shape. The shell is thin and the inner surface smooth. The peristome is holostomatous. The growth lines are fine to moderately strong, prosocyrt.

Remarks. Small specimens of this taxon are fairly common in the Insect Limestone.

Genus Hippeutis Charpentier, Reference Charpentier1837

Synonymy. Hippeutis Gray, Reference Gray1857.

Type species. Helix complanata Linnaeus, Reference Linnaeus1758, by subsequent designation by Clessin (Reference Clessin, Küster, Martini and Chemnitz1886).

Diagnosis. Planispiral, small sized, whorls carinated, aperture oblique, subcircular-oval.

Occurrence. Paleocene to Recent, Europe, North Africa and Asia.

Hippeutis headonensis (Jodot Reference Jodot1942)

Plate 1, fig. 12

1. 1852 Planorbis lens sensu Edwards non Brongniart, p. 104, pl. 15, fig 8a–d.

2. 1891 Planorbis lens Brongniart; Newton, p. 282.

3. 1901 Planorbis lens Brongniart; Newton, p. 67.

4. 1942 Planorbis (Hippeutis) headonensis, Jodot, p. 175.

Lectotype. NHMUK G.71081a Edwards Collection, Natural History Museum, London. Edwards (Reference Edwards1852) pl. 15, fig 8a. Paralectotypes, six specimens NHMUK G.71081 b–g, Edwards Collection, Natural History Museum, London.

Type horizon and locality. Headon Hill Formation, Headon Hill, Isle of Wight.

Referred material. IWCMS.2007.11 Sticelets, Thorness Bay, Isle of Wight; IWCMS.2007.14 Saltmead, Thorness Bay, Isle of Wight.

Diagnosis. Small, planispiral, midline of whorl with sharp carina.

Distribution. Headon Hill Formation, Bembridge Limestone Formation (Solent Group), Bembridge Marls Member and Hamstead Member (Bouldnor Formation, Solent Group), Isle of Wight and Hampshire, southern England.

Description. Small-sized, up to 8 mm in diameter, height up to 1.5 mm. Planispiral in shape. Teleoconch of up to four shallowly convex whorls, of which the abapical surfaces are more convex. Above the midline of the whorls there is a rounded carina, giving the whorl an angular shape. The adapical surface is shallowly convex, the abapical side is less shallowly concave. The suture is strong, grooved. The whorls expand rapidly. Protoconch obscured.

The whorls are the same shape as the aperture which is flattened oval in outline. The shell is thin and the inner surface smooth. The peristome is holostomatous. The growth lines are fine to moderately strong, prosocyrt.

Remarks. Edwards (Reference Edwards1852) discussed at length the identity of this shell, concluding that it was identical with Planorbis lens Brongniart, Reference Brongniart1810. Jodot (Reference Jodot1942) observed that the carina in Planorbis lens Brongniart, Reference Brongniart1810 is sharper, the whorls less convex and the sutures less pronounced than those seen in the English shells; there does however seem to be no difference in the position of the carina in both forms. Edwards makes reference to the illustrations of P. lens by Deshayes (Reference Deshayes1837 vol 2, pl. IX, figs 11–13) which show a much flatter shell than the specimens from the Solent Group, supporting Jodot's conclusion (Reference Jodot1942). It is uncommon in the Insect Limestone.