The newly liberated medusa of Perigonimus muscoides M. Sars has been found to be a Bougainvillia. A specimen from the plankton points to the extreme probability that it can be regarded as synonymous with a previously described medusa, B. nordgaardi (Browne). The name of both hydroid and medusa now becomes B. muscoides (M. Sars 1846).

The systematic importance of the above discovery is discussed, and the genus Rhizorhagium M. Sars 1877 is redefined to include all those species of “Perigonimus” with fixed gonophores, viz. Rhizorhagium roseum, R. sarsi, R. antarcticum, R. formosum, and a new species, R. album, from the Cornish coast.

Variations in the form of the hydroid of Leuckartiara octona are described. The newly liberated medusa of Perigonimus abyssi G. O. Sars is figured for the first time and the species referred to the genus Leuckartiara.

A new Bimeria-like hydroid, Thamnostoma russelli, is described. The characters of the medusa indicate that it belongs to the genus Thamnostoma Haeckel, and the characters of the hydroid show that the genera Thamnitis and Thamnostoma must be united.

Corymorpha annulicornis M. Sars is redescribed from living specimens and the medusa is shown to be Euphysa aurata Forbes. It must henceforth be known as Corymorpha aurata (Forbes).

A new species of Campanulina, C. paracuminata, with its young medusa is described from Plymouth.

Notes are included on Boreohydra simplex, Stauridium productum and Staurocoryne filiformis.

Certain points in the synonymy of all these species are discussed.

A local race of Idotea viridis from south-east Essex is described and its classification as /. viridis discussed. This animal is a nektonic form and so far has only been found in New England Creek in south-east Essex. The biology and post-embryonic development of this race is described. Quantitative samples were taken of the animals present in the creek in 1934, 1935 and 1936. I. viridis was rare in the first five months of the year; numbers rose to a maximum in late June and July and remained comparatively high until the end of October.

The number of young in the brood pouch is very variable. There is some evidence that the number of fertilized eggs was reduced by the expulsion of embryos before their development was complete. The newly hatched I viridisis described.

A study made of the adaptations to tubicolous life found in the small brackish water Photid Amphipod, Leptocheirus pilosus Zaddach, revealed several interesting points.

The presence of cement glands in many amphipods has been recognized by several previous authors. In L. pilosus these glands are found mainly in the upper joints of the first two pairs of peraeopods, opening to the exterior through a common duct in the claw. Unicellular glands are also found all over the body, particularly on the coxal plates.

An analysis is made of the mysids which occurred in a series of bottom stramin net plankton hauls made at three stations in the Plymouth area in 1927–8.

There were two marked maxima in numbers of mysids, a summer one in July and August, and a winter one in December and January.

The summer maximum was due entirely to Leptomysis gracilis.

The winter maximum was due mainly to Schistomysis ornata and Anchialina agilis, but the two species of Gastrosaccus, and Neomysis longicornis also contributed to a lesser degree.

The summer maximum was composed mainly of adult males and breeding females of Leptomysis gracilis which appear to become markedly planktonic in habit at the breeding season though keeping to the deeper layers. Immature specimens were present but the majority were probably higher up in the water (mid-water).

There is a suggestion that a similar planktonic habit is to be found in Schistomysis ornata and Anchialina agilis during their breeding period in the winter, but it is not nearly so marked as in Leptomysis gracilis.

The winter maximum is mainly due to large numbers of immature forms and it is suggested that environmental factors, probably temperature, cause a concentration of immature stages in the bottom water during winter. At other times of the year these immature forms are distributed over a much greater depth range of water.

Idle swimming movements just over the bottom are a normal habit of bottom living mysids.

The collection provides evidence of three types of movements in mysids: (i) idle swimming just over the bottom, (ii) definite and marked movements into the plankton in the adult condition during the breeding season, and (iii) movements of the immature forms to greater or lesser depths according to environmental conditions, probably temperature.

In a previous paper (Moore, 1936) an account was given of certain variations in the shape and colour of the shell in Purpura, and it was pointed out that these variations are apparently controlled by diet. It was shown that growth ceases at the onset of sexual maturity, and at the same time other changes such as the thickening of the edge of the shell take place. It was shown also that both the proportion of the population exhibiting these changes, and the average size at which they occur, vary considerably from one locality to another, this variation also being apparently correlated with the nature of the animal's diet. The present paper consists of a study of the growth of the shell and soft parts and an attempt to show whether the observed differences in size at sexual maturity in different populations are to be accounted for by differences in the growth rate during the growing phase.

The copepods described in this paper come from two sources, the Firth of Clyde and the St Lawrence River. Several new species were collected from Balloch Bay on the Greater Cumbrae in 1935 and 1936 during an attempt to obtain some of the early species described from Scottish waters. The remainder were collected while working at the Biological Station at Trois Pistoles, Quebec, during a visit to Canada in 1937. The environment in Balloch Bay is composed of a fine muddy sand, strewn with boulders. The bay is on the eastern side of the island and therefore in a sheltered position. A description is given in Appendix III of The Biology of the Sea Shore, by Flattely & Walton (1922). The conditions under which the Canadian material was found will be dealt with in a later paper describing the remainder of the collection from the St Lawrence; it will be sufficient here to state that the conditions are essentially marine.

Copepods from three allied genera are included here: Paramesochra T. Scott, 1892; Leptopsyllus T. Scott, 1894; and Remanea Klie, 1929. The first two have for some time been in a state of considerable confusion and it has been a matter of some doubt into which genus the various species should be placed. Several efforts have been made to clarify the position (notably by Klie, 1929 and Monard, 1935) but the more recent work of Kunz (1938) has produced a clear separation based on the presence or absence of an endopod on the second leg.

The eggs of Purpura are laid in vase-shaped capsules, attached in clusters to the rocks. Spawning takes place throughout the year, but chiefly in the winter and spring (Pelseneer, 1935; Moore, 1938; Colton, 1916). It is said to take more than an hour to produce one capsule, and 24 hr to produce ten (Pelseneer, 1935, p. 508), and the number of capsules laid at one time is said to average fifteen, and to range from six to thirty-one (Pelseneer, 1935, p. 490). Cooke (1895, p. 124) states that a single Purpura produces as many as 245 capsules. The capsules contain a large number of yolky eggs, the estimates of the numbers of these per capsule varying from three hundred to a thousand (Colton, 1916; Pelseneer, 1935, p. 527). Most of these ova are unfertilized and serve as food for the few embryos which develop: five to forty according to Pelseneer (1935, p. 481), ten to twelve according to Colton (1916). The time of development is about 4 months (Pelseneer 1935, p. 527). The capsules are laid in crevices in the rocks, or sometimes under stones, but at the same tidal level as that inhabited by the adults. The young, when hatched, are generally supposed to retreat into cracks in the rocks, presumably at the same level, and Colton states that they feed there on small Mytilus.

Although the medusa Dipurena halterata (Forbes, 1846) is well known, and has been figured by a number of authors (e.g. Forbes, 1848; Browne, 1897), the hydroid of this peculiar species has remained unknown. This medusa is rather scarce at Plymouth (Russell, 1938). On May 3 1938 I had the good fortune to find at Plymouth a small hydroid of the Syncoryne type which later liberated young medusae, and these proved to be young specimens of Dipurena halterata.

In a former paper (1929) it was stated that “regeneration takes place easily at the posterior end of divided syllids, but on cutting the most anterior part, the chitinous tube and massive proventriculus of the pharynx hinder the process of closing the wound and subsequent regeneration fails in most cases”. The minimum length of so-called head pieces, in which regeneration of the tail can be effected, always comprises at least one or two more segments than those constituting the pharyngeal region. This length is internally occupied by a large chamber containing a series of highly specialized organs of ectodermal origin, extending as far as the first appearance of the moniliform intestine in a segmental cavity, which is separated from the previous one by a complete septum.

The nematocysts of the three species of Leptomedusae, Aequorea forskalea, A. vitrina, and A. pensilis, and of the two siphonophores Agalma elegans and Velella velella are described.

The specific characters of the three species of Aequorea are discussed and it is shown that A. pensilis is probably the same species as A. macrodactyla

In the flounder adipose tissue forms a padding between the muscles to the dorsal and ventral fins. A little is present under the skin, more especially where the lateral line septa and the myocommata meet the skin. In addition a quantity of fat is associated with the skeleton.

Immature flounders living in the estuaries of the Tamar and Lynher are fattest after intense feeding during the summer, and leanest after the winter fast.

Maturing flounders have a high fat content before going to sea to spawn. While in the sea during the spawning season, February to April, very little feeding takes place and there is a rapid drop in fat content. Spent fish are very lean.

Those females which return to the estuaries after spawning rapidly make good their fat loss.

A single specimen of the rare thalassinid Jaxea nocturna was recently dredged from mud off Rame Head, Devon, by S.S. Salpa on September 3 1937 during the September Vacation Course at the Plymouth Laboratory. Prior to this there are only four records of the adults of this species in waters round the British Isles although they are abundant in the Adriatic Sea. Selbie (1915) summarizes the British records as far as 1914. The first individuals were taken as fragments from the stomachs of gurnards and Pleuronectes cynoglossus captured in the Firth of Clyde near Ailsa Craig (Scott, 1899); the next was from the Irish Sea, in mud, offClogher Head, Co. Louth, at a depth of 32½ fathoms and in 1908 one was taken in Loch Fyne in 34 fathoms. The next record is a single specimen taken by Mr G. A. Stephen on March 26 1936 from the mud two miles south of Rame Head, and at a depth of 24 fathoms. Since September 3 1937 four more have been captured in the same locality, one on September 28 1937 and three on October 6 1937, using a new type of dredge.

The 37 sq. miles of intertidal banks in the Mersey Estuary have been surveyed and classified according to their nature and fauna.

Half the banks occur in the Outer and half in the Upper Estuary. Four-fifths of the total area is composed of sand and most of the remaining one-fifth of mud occurs in the Upper Estuary.

The burrowing fauna of the Outer Estuary is abundant and varied; that of the Upper Estuary is abundant but not varied.

The distribution of species in the Mersey Estuary is similar to that in the estuaries of the River Tees and Tay, except that in the Mersey Estuary a sudden drop in the numbers of species occurs at Rock Light. This is attributed o t the strong tidal streams in the Narrows.

The densely inhabited banks of the Upper Estuary are mainly composed of mud and are situated high in the shore zone. In the Outer Estuary the densely inhabited banks are of muddy sand with some banks of mud and are situated near the low-water mark in sheltered positions.

The burrowing species of the Upper Estuary also occur, with many others, in the Outer Estuary.

The observations described in this paper were made during an investigation of the estuary of the River Mersey by the Water Pollution Board of the Department of Scientific and Industrial Research and the results are published by permission of the Department.

The present report continues the series of observations on the seasonal abundance of the pelagic young of teleostean fish in the plankton off Plymouth (Russell, 1938b), and gives the results for the year 1938. These results are published in the same form as in previous reports. The dates on which collections were made with the 2 m. stramin ringtrawl are given in Table I, and the monthly average catches of the young fish per half-hour oblique haul in Table II.

1. The photographic neutral-tint wedge method of measuring the total illumination falling on an area over a long period of time is described.

2. A study is made of the chief sources of error inherent in photographic methods, i.e. (a) the uncertainty in the value of the wedge constant, and (b) the failure of the reciprocity law, in that the amount of blackening of the photographic emulsion is not, in general, strictly proportional to the product of the intensity of the illumination and the duration of the exposure.

3. It is shown that P.O.P. obeys the reciprocity law sufficiently closely for durations of exposure between 1 and 24 hr. Gaslight paper, on the other hand, can only be used when the duration of exposure is less than about I hr.

4. It is shown that when P.O.P. is used, and a sheet of diffusing glass is placed above the wedge, the value of the wedge constant is sensibly independent of the direction and quality of the incident light.

5. Spectral sensitivity curves to tungsten filament light for gaslight paper and P.O.P. have been evaluated. From these, and other data, correction factors have been calculated for converting the photographic measurements of illumination into visual units.

6. It is concluded that the method is sufficiently reliable for use in the field, where its simplicity and the small amount of apparatus required, make it specially suitable. The experimental uncertainty is about ±5 to ±10%.

Analyses of phosphorus, nitrogen, iron and manganese are recorded for Balanus nauplii (a cirripede crustacean), post-larval Callionymus (a teleostean fish), mature Sagitta elegans (a chaetognath), Pleurobrachia (a ctenophore) and for crab zoeas and megalopas (Table I). A sample of Sagitta setosa in 1934 contained much more iron than that in S. elegans here reported. The ctenophore, Pleurobrachta, is relatively poor in phosphorus, nitrogen and iron and its ash-free protoplasm must evidently be rich in either fats or carbohydrates. Neither Pleurobrachia nor Balanus nauplii effect any appreciable concentration of manganese from sea water.

A study of the larval stages of different lamellibranchs from Plymouth with a view to determining their importance in the plankton has brought out some interesting facts. It is well known that the free-swimming larvae are much simpler than most of the gastropod veligers, and that the velum is usually entire, having rarely a slight indentation, showing a tendency to be bilobed in the larger forms. They thus resemble in this respect the primitive gastropods. In many of them the velum is lost early in life, and usually the change in form of the shell takes place after metamorphosis. The post-larval growth is therefore an important part of the life history. The first shelled stage is so similar in all species that it is almost impossible to distinguish the different early veligers in the plankton, but in certain cases fertilizations have been made and the larvae reared until they have lost the velum and descend to the bottom when the species, or at least the genus, can usually be identified.

New values for the extinction coefficient of red light in distilled water require that published results for this coefficient in waters from the Tamar Estuary shall be increased by o.1, 1.3 and 2.0 at 610, 720 and 750 mμ respectively. Earlier deductions as to the favourable transmission of red light in turbid estuarine waters apply only up to about 680 mμ. That part of the extinction coefficient due to suspensoids and colouring matter was inversely proportional to the first power of the wave-length. Other conclusions remain unaffected.

The plankton collected at a station in the Bristol Channel in 1936-7 is related to chemical and hydrographical factors.

On account of the varying speeds of the tidal streams, the observations refer, not to a single point, but to a series of points along a length of the channel. Gradients of salinity, phosphate, and a possible complicated gradient of oxygen saturation, were determined, and, from the average monthly salinities, an annual cyclical movement of water deduced.

The nematocysts of twenty species of Hydromedusae occurring at Plymouth are described. Of these, twelve were Anthomedusae and seven were Leptomedusae, and one was the Siphonophore, Muggiaea atlantica. The medusae fit very well into the generally accepted classification as regards the types of nematocysts they possess.

Lar sabellarum, the hydroid of Willia stellata, has a type of nematocyst not found in the other species—a macrobasic mastigophore. This is a further justification for the formation of a separate family, the Williidae, to hold this species and its relations.

While the Anthomedusae are clearly split up into distinct groups as regards their types of nematocysts, the Leptomedusae form a single group.

It is suggested that the so-called acrophores and anacrophores recorded in siphonophores may be merely stages in the development of other nematocysts.

It is urged that much more research is required on variation in size and structure of nematocysts in individual species before they can be used as specific characters for separating doubtful species.