The Plymouth Fauna List contains records of two genera of pteropods, Limacina and Clione. Of the first, Limacina retroversa (Flem.) is by far the better-known species, apparently occurring regularly at Plymouth in large numbers in townettings from outside, and sometimes inside, the Sound. It breeds at Plymouth from June to August, and Lebour (1932) has given a detailed account of its breeding and larval stages and has discussed its role in the plankton. The second species of Limacina at Plymouth is lesueuri (d'Orbigny), which has been observed from time to time since 1906, when it was very common. The last record in the Fauna is off the Breakwater in 1920. Of the gymnosomatous pteropods, Clione limacina Phipps is the only species regularly occurring. Lebour (1931) has described the life history of this form, and mentions February to August as its months of greatest abundance. Its breeding season is June to August. Another gymnosome, tentatively referred to as Clionina longicauda, is reported by Russell (1936), and from the specimen department at Plymouth Laboratory the writer obtained some preserved specimens, not easily identifiable, of a Pneumodermopsis taken locally; its species is perhaps ciliata, recorded by Massy (1917) from the Irish Coast.

The breakwater in Plymouth Sound offers a simple case of two adjacent populations ofintertidal organisms subjected to quite different degrees of exposure to wave-action. The other environmental factors, with a few exceptions, are approximately the same each side, and the effects of the wave-action should be clearly demonstrable.

Acteon tornatilis is an opisthobranch mollusc which burrows in sand, using foot, labial and cephalic tentacles in the process. The last also help to exclude sand from the mantle cavity, which is extended into a caecum coiling alongside the visceral hump, presumably used for respiration but also for excretion. The main pallial water current is an exhalant one on the right.

The mantle skirt carries, on the left, numerous repugnatorial glands with toxic secretions.

Labial glands lie at the mouth and the buccal cavity contains jaws and a reduced buccal mass and radula. Into it open salivary glands the structure of which is like that of the pyramidellids. The oesophagus shows traces neither of glands nor of torsion whereas the stomach, though simplified, has resemblances to that of a prosobranch.

The reproductive system is shown to be different from previous descriptions. Male and female ducts are separate from the lower end of the little hermaphrodite duct. The former passes to a prostate from which a vas deferens leads to a large uninvaginable penis; the latter has associated albumen and mucous glands and there is a receptaculum seminis to the duct of which a ventral channel leads from the female aperture in the mantle cavity.Discussion of these aspects of the animal's structure confirms its position as the most primitive of the opisthobranchs.

When Michaelsen (1923) described a species of didemnid from Heligoland, he stated that it was very similar to Leptoclinum maculosum Milne Edwards (1841), so far as may be judged by external appearance, but since no adequate description of this latter existed he proposed to call his Heligoland form by a new name, Didemnum helgolandicum, rather than use an old name which might well be wrong. Neither Michaelsen nor Hartmeyer, who described further details of D. helgolandicum (1924), was able to compare it directly with specimens of D. maculosum from the Channel coasts whence it was first described by Milne Edwards. Through the kindness of the directors of the Zoological Museum of Copenhagen and of the Biological Station of Roscoff I have been able to obtain specimens of both these forms and to compare them with specimens collected around Plymouth and on the coast of North Wales, and with specimens of D. candidum Savigny, collected at Naples, and from the Red Sea, and of Trididemnum alleni Berrill, collected around Plymouth.

Leptoclinides faeröensis Bjerkan (1905) is a little-known boreal species which has been found only in the Atlantic Ocean (Fig. I). The most northerly record is from a little south of Spitzbergen, the most southerly from 37° 08' N., off the North American coast. It occurs on the coast of Norway and in the Faeroe Islands, but it has not been reported nearer to Plymouth than these two localities. Most records are from deepish waters, though it occurs in the sublittoral zone along the Norwegian coast. It was in this zone, at Looe Island (50' 20' 24“ N., 4 °26' 53” W.) near Plymouth, that we found a specimen of this species growing on a rock about 80 cm. below O.D.—just sufficiently low for it to remain covered by a few centimetres of water at the lowest tide of the year, the equinoctial spring tide.

On 26 November 1953 the new research ship Sarsia on her first cruise collected a number of Pontophilus echinulatus (M. Sars) (with an Agassiz trawl, depth 100 fm., La Chapelle, Bay of Biscay). Mr G. R. Forster, of the Plymouth Laboratory, noted that these did not fit into the key given by Kemp (1910) in that they have in the male a distinct appendix interna at the base of the four last pairs of pleopods, while in the female this is absent, the inner ramus being usually undivided, although occasionally an indistinct division can be made out. Otherwise they agree with Kemp's diagnosis.

Kemp (1910) notes M. Sars 1861 as authority, but this is only a preliminary description. In Sars (1868), given in Kemp's (1910) bibliography but not under the species, it is seen that he describes both male and female exactly as in the specimens from Sarsia, the male having a distinct appendix interna on the last four pairs of pleopods and an appendix masculina also on the second pair, the female pleopods having very short inner rami, except in the first which is long, and there is no appendix interna. Sars's figures of these limbs are very good. Kemp (1911) joins Philocheras with Pontophilus, and in this he is now followed by most authors.

Kemp (1916) reviewed the pleopods in the genus Pontophilus, as far as he could with the material he had in India, and he proposed certain groups according to the presence or absence of the appendix interna.

Since I first found Trididemnum niveum (Giard) at Salcombe in the autumn of 1951 (Carlisle, 1953) this species has spread and increased greatly in the Plymouth area. I have found it in abundance at Salcombe (Castle rocks and the Salstone), Wembury, and especially at Looe around the Island. The favourite habitat at all these places is the same as that at Roscoff, on the fronds of Cystoseira. It occurs rather less frequently on the holdfasts of Laminaria ochroleuca and occasionally on other species of Laminaria, but very little on any other substrate. It is not truly intertidal; the majority of specimens are to be found just below low-water mark of spring tides, and very rarely are any seen above low-water mark of even the lowest tides of the year.

Milne Edwards (1841) established the genusLeptoclinum for those Didemnidae which possessed a largely expanded common cloacal system. His type of the genus wasL. maculosum which is now placed in the genusDidemnum Savigny (1816). Other species wereL. asperum andL. durum which are now regarded as mere forms ofDidemnum maculosum (e.g. Harant & Vernièeres, 1933); Leptoclinum fulgens which is closely related (see Harant & Vernièeres), if not a mere colour form ofDidemnum maculosum], Leptoclinum listerianum which has been transferred to the genusDiplosoma Macdonald; andLeptoclinum gelatinosum. This last has often been considered synonymous withDiplosoma listerianum, but my reasons for disagreeing with this assumption are elsewhere expressed (Carlisle, 1953). Milne Edwards did not of course describe the course of the sperm duct by whichDiplosoma is distinguished fromDidemnum. In the absence of a description of this diagnostic character we are reduced to a consideration of numerous details of the anatomy of Leptoclinum gelatinosum in order to decide where to place it in the classificatory scheme. When such a point-by-point comparison of shape and curvature of the gut, position of anus, form of atrial and buccal apertures, nature of test, etc., is made, it appears that the one point in which the drawings and descriptions given by Milne Edwards differ betweenL. gelatinosum andDidemnumgelatinosum Mime Edwards (1841) is the presence of a common cloacal system in the former and its absence in the latter. But the presence or absence of a common cloacal system is no longer regarded as a generic distinction (see, for example, van Name, 1945).

Results are given for measurements of fat, vitamin A and carotenoids in groups of Meganyctiphanes norvegica, Thysanoessa raschii, Crangon allmani, C. vulgaris, Nephrops norvegicus and eyes of Homarus vulgaris, collected at regular intervals for a year or longer.

In both species of euphausiids vitamin A was consistently present mainly in the ester form and concentrated chiefly in the eyes. More than half the total astaxanthin was in the eyes. No other carotenoids were detected.

Astaxanthin and vitamin A were accumulated by the euphausiids more rapidly during the spring and autumn-feeding periods associated with diatom outbursts than at other seasons. There was a delay in Thysanoessa raschii, but not in Meganyctiphanes norvegica, between resumption of more rapid growth during spring and autumn and increase in concentration of vitamin A and astaxanthin. The difference was possibly due to differences in diet of the two species in relation to the seasonal biological composition of the plankton.

In the euphausiids, concentrations of vitamin A and astaxanthin were much higher in larvae and in adults over 30 mm long of M. norvegica, and in larvae and adults over 15 mm of Thysanoessa raschii, than in mature adults of Meganyctiphanes norvegica of 20–30 mm and Thysanoessa raschii of 13–15 mm, respectively. An inverse relationship between fat and vitamin A concentration was noted in both species throughout the year.

In Crangon spp. and Nephrops norvegicus there was no evidence of any seasonal variation of either vitamin A or carotenoids. Differences in the carotenoid metabolism of the two species of Crangon are discussed.

This paper is the second of a series dealing with the annual cycle of growth andreproduction in British ascidians; a previous paper (Millar, 1952) dealt with the speciesDiplosoma listerianum (Milne Edwards), Ciona intestinalis (Linnaeus),Ascidiella aspersa (Muller), andBotryllus schlosseri (Pallas)

The present investigation is concerned with the growth, the course of sexual reproduction and establishment of new generations, and the histological changes in the gonad throughout the year, in the ascidianDendrodoa grossularia (family Styelidae).

Samples were examined from two widely separated localities: Fambridge in the River Crouch, Essex; and Farland Point, Isle of Cumbrae, in the Firth of Clyde. The specimens from Essex were dredged from a depth of about 2 m. (below L.W.O.S.T.), and were attached to the empty shells of the European oyster,Ostrea edulis L. and to the shells ofCrepidula fornicata L. The speci-mens from the Firth of Clydewere attached to stones on sheltered parts of the shore. The animals here extended over a zone of the shore from about Chart Datum+ 2.5 ft. (0.76 m.) to about Chart Datum+ 7.5 ft. (2.29 m.): Only in very sheltered positions, such as under large boulders, did Dendrodoa occur in abundance. The two habitats were thus very different in nature, one being sublittoral on the south-east coast of Britain and the other being littoral on the north-west coast. The value of comparisons is limited by the different nature of the conditions to which the sublittoral and the littoral populations were exposed.

The observations on growth in the Clyde extended over most of 1951 and 1952, and nineteen samples were taken.

Twenty-five years ago I published a note (Atkins, 1929) on a then unnamed member of the Saprolegniaceae, a destructive fungal parasite of the pea-crab, Pinnotheres; the name Leptolegnia marina is now proposed for this fungus.

Styela mammiculata n.sp. is based on four specimens collected in the Plymouth area during the summer of 1953. The most noticeable external feature is the extensive mammillation of the test. The mammillae are much smaller than those of Phallusia mammillata and deserve to be called rather ‘mammiculae’.

Of the four specimens, two were taken from Drake's Island buoy (National Grid Reference, 20/4753)m Plymouth Sound, growing about half a metre below the water line, and two from the oyster bed of the Lynher river estuary, near Antony Ferry (National Grid Reference, 20/4257), growing about 12 m. below low-tide mark attached to oyster shells. The largest specimen was from the latter locality and measured III mm. long in the contracted, fixed condi- tion. The smallest, from Drake's Island buoy, was 54 mm. long.

Many brachyuran megalopae swim with the legs disposed in a curious manner. The chelipeds and first two pairs of walking legs are folded tightly beneath the body, while the two posterior pairs are wrapped over the dorsum, the third pair being stretched out anteriorly, the dactylus, according to its length, touching or being looped round the eye-stalk. It is suggested that this posture gives stream-lining to the megalopa and improves its swimming. The described arrangement has been observed in all but three of some twenty-five species occurring at Plymouth.

In the three exceptions, Corystes cassivelaunus, Thia polita and Pinnotheres pinnotheres (= veterum), all legs are carried folded beneath the body.

Reference is made to previous descriptions of the folding of the legs in the brachyuran megalopa.

For nearly fifty years a small marine organism has been cultured at the Marine Biological Association's Laboratory at Plymouth, mainly to be used as a food supply in rearing marine larval forms.

The cultures were originated by the late Dr E. J. Allen in 1907. The first record of these cultures and the methods used to maintain them were published by Allen & Nelson (1910) in a paper describing methods for obtaining persistent cultures of eighteen species of plankton diatoms. One of these cultures flourished so successfully that subcultures have been distributed to many laboratories and institutions both in Europe and America. This organism was named Nitzschia closterium W. Sm. forma minutissima. The authors, however, did not describe the organism or produce an illustration, so the combination can be considered only as a nomen nudum.

In previous publications the author (Black, 1948a-c, 1949, 1950a) has reported the seasonal variations in chemical composition that occur in certain of the common Phaeophyceae. In the sublittoral and littoral zones it has been found that a correlation exists between the chemical composition and the depth of immersion of the plant (Black, 1950&, and unpublished work). Differences in composition, particularly during the summer months, also occur in the same species taken at the same time and depth but from different habitats (Black, loc. cit.), and there is also evidence that in the laminarians the stage of development of the plant has a profound influence on the composition. In all the above-mentioned analyses the entire plants have been separated into stipe and frond, dried under controlled conditions, milled, and a well-mixed representative sample of each taken for analysis.

It has long been recognized that a proper knowledge of the fauna of submerged rocks can be obtained satisfactorily only by direct study with diving apparatus (Gislen, 1930; Kitching et al., 1934). Although the latest methods of indirect underwater observation, photography and television, may be useful on a smooth sea floor, they can give little information about a rocky area owing to their inability, as yet, to look underneath a boulder or an overhanging ledge. The superiority of the ‘submarine biologist’ over the indirect methods lies in the fact that he can readily collect samples for positive identification, or mark individual organisms for further study; though at present, unless very expert, he is limited to depths of under 20 fathoms. The successful use of free-diving apparatus for biological work is well established. Five years ago Prof. Drach with Cousteau's now famous ‘aqualung’ investigated the sublittoral fauna of various rocky shores, reaching a depth of 30 m. (Drach, 1948). Much additional work has been done in the Mediterranean and other warm seas, while farther north Bainbridge (1952) used a Siebe-Gorman apparatus to study the behaviour of plankton in the Clyde.

Recently I have reported experiments which have led me to throw doubt on the universal applicability of the theory of the production of a moult-inhibiting hormone by the eyestalks of the decapod Crustacea (Carlisle, 1953). I suggested that the eyestalk moult-inhibiting hormone might be associated with the existence of a definite moulting season. In animals which possessed such a moulting season moultingwould then be inhibited outside this season, but within the season there might well be no such inhibition. The experiments reported here support a modified form of this hypothesis.

Comments on the uses of penetrometers in general are followed by remarks upon an earlier one for use on dry beaches. Some discussion is given of the behaviour of beds of sand disturbed by shocks and converted thereby into a state of quasi-liquefaction. Finally, a description is given of a tall pull-down penetrometer which can be used on beaches covered by modest depths of water.

Through the kindness of Dr L. H. N. Cooper of Plymouth I have been given the opportunity of examining some of the plankton samples taken by Surg.-Lt. P. Campbell, R.N.V.R., of H.M.S. Challenger. It is hoped that the results of these and later surveys will be published elsewhere in more detail, and in association with those made by the Scottish research vessels farther north, but two records of unusual interest are brought to notice here. The collections so far examined in detail were taken during April and May 1953, on a line of stations west of the English Channel, from 49° 39′ N., 3° 30′ W. to 47° 16′ N., 17° 52′ W. between 15 and 19 April, and on the return line from 47° 50′ N., 17° 40′ W. to 49° 28′ N., 5° 52′ W. between 25 and 28 May. They were made by 10 min. horizontal hauls at 30 fathoms depth.

If a male dogfish is held in the hand and its belly stroked firmly backwards with the ball of the thumb a fluid can be expressed from the cloaca. In my experience this fluid in a fresh animal invariably contains sperm, whatever the season of the year. After a period of inanition, however, sperm eventually disappears from the cloacal fluid. Such an animal is a convenient test object for gonadotropic activity by a method which closely parallels the toad-pregnancy test of Galli Mainini (1947).