Lasaea rubra, like other small Erycinacea, is unusual among eulamellibranchs in its relatively great mobility on the surface of the substrate. It can crawl about as freely as a small gastropod and lays down a mucous trail for the attachment of its progressing foot, drawing the shell and body rhythmically forward after each advance thrust of the foot. Unlike some other Erycinacea, L. rubra has no well-defined sole; it attaches by the sharp lower edge and part of the side of the foot, which is strongly ciliated and well supplied with mucous glands. In most burrowing eulamellibranchs, the site of communication with the surrounding water has shifted to the paired siphons at the posterior end. The Erycinacea, however, have an anterior inhalant siphon; and—as in forward moving prosobranch gastropods (Morton, 1958)—there is an obvious adaptive advantage in receiving the ingoing current from the water into which the animal is moving.

Relative spectral emission curves are available for the lights of many invertebrate animals, but none exists for fish. It seems likely that many bony fish use their photophores to signal to one another. Information about the spectral composition of fish luminescence is desirable to permit comparisons with the spectral sensitivities of fish eyes, to enable calculations to be made of luminous intensities, and to allow estimates to be made of the rate of attenuation of such lights in sea water. To further these ends, measurements were made of the spectral composition of the luminescence of the lantern-fish, Myctophum punctatum.

The last of the organisms to be studied in this series was chosen as a representative of the Dinophyceae. The treatment of Prorocentrum micans Ehrenberg has been similar to that of Asterionellajaponica Cleve & Müler ex Gran (Kain & Fogg, 1958 a) and Isochrysis galbana Parke (Kain & Fogg, 1958 b). The present paper includes a discussion of the results for all three organisms in the light of work by previous authors.

The widespread occurrence of sulphatases in the Mollusca was first demonstrated by Soda & Hattori (1933 a, b) who showed that these enzymes are mainly concentrated in the digestive glands. That extracts from marine molluscs also possess β-glucuronidase activity was first noted by Dodgson, Lewis & Spencer (1952) who studied the optimum conditions for the activity of this enzyme and arylsulphatase in Patella vulgata (L.) and Littorina littorea (L.) and applied their findings in an investigation of the distribution of both enzymes among various other marine molluscs (Dodgson, Lewis & Spencer, 1953).

Mites of the family Halacaridae are abundant on the sea shore, and in the sea down to considerable depths. Their identification is not an easy matter; there is no one account which can be used to identify all the British species, and the use of any one of the general accounts of European species, such as André (1946) or Viets (1936), by itself might easily lead to misidentification.

The purpose of the present list is to record the species which have so far been found around the British Isles, and to indicate sources of reliable descriptions of each species. A list of the British species of this family was given in a general list of British Acari by Turk (1953), and this has provided the starting point for the present list; no reference to occurrence in Britain before Turk's list is given, apart from one by Halbert (1920) which was left out by Turk. Twelve of the thirty-six species in the present list were not recorded by Turk. One species, Halacarus zosterae (Fab.), recorded by Turk has been omitted because the original description is quite inadequate to decide even which genus the creature should belong to. Eight species are known from British fresh water; these have not been included in the present list.

A new species and genus of brachiopod has been dredged by R.V.‘Sarsia’ on three cruises to the Western Approaches of the English Channel and two to the La Chapelle Bank region. In general appearance it closely resembles Dallina septigera (Lovén) with which it appears to have been confused by Fischer & Oehlert (1891).

In 1956 it was obtained on 13 June at position 48° 33′ N., 10° 05′ W. at a depth of 570–770 fathoms, four specimens of shell length 17–25 mm were taken together with seven D. septigera.

The discovery of a homoeomorph, Fallax dalliniformis, of Dallina septigera (Lovén) dredged with that species (Atkins, 1960) and, it is believed, sometimes confused with it, certainly by Fischer & Oehlert (1891), has made a brief redescription desirable. During the present work more than a hundred D. septigera of shell length 5–31 mm have been obtained, and most of them examined internally.

The original description in Latin—without figures—of Dallina septigera (= Terebratula septigera) was by Lovén in 1846 (p. 183). Unfortunately his description does not now clearly separate his species from Fallax dalliniformis, except perhaps his failure to mention the presence of dental plates, pedicle collar and spiculation. It is doubtful how much weight can be attached to this, for on the same page he failed to mention the presence of dental plates in Macandrevia cranium. He gave the length as 28 mm, width as 21.5 mm and depth as 17 mm.

The family Entoniscidae (Isopoda-Epicaridea) is included in the superfamily Bopyrina, which comprises the families Bopyridae, Dajidae and Entoniscidae. The Bopyridae are parasitic in the branchial cavity or on the abdomen of decapods, mainly Macrura and Anomura. The Dajidae occur in the incubatory chamber or on the dorsal surface of mysids and euphausiids, and rarely on Brachyura. The Entoniscidae are found in the visceral cavity of Anomura and Brachyura (an exception is Synalpheion, in a macruran, Coutière 1908), surrounded by a membrane of host origin, and communicating with the branchial cavity of the host by a pore. Together with this internal habitat the family has extreme morphological specialization. Females of the Bopyridae have distinct thoracic segmentation and well-developed peraeopods; in the Dajidae the peraeopods are distinct, but segmentation is less evident; in adult females of the Entoniscidae, however, the peraeopods consist of only the enlarged oostegites, with rudimentary endopodites in some species, and the thorax has only traces of segmentation.

The piddock, Pholas dactylus L., gives off a luminous secretion when irritated. The luminous glands which produce the secretion are two longitudinal stripes in the exhalant siphon, a pair of triangular organs in the mantle cavity near the base of the siphon, and a stripe around the ventral rim of the mantle (Panceri, 1872).

The histology of the light-organs has been described several times. A light-organ is covered by a simple columnar ciliated epithelium, below which are many glandular cells, which discharge through the surface epithelium. The outer part of the glandular layer consists of a mass of large mucus cells. Deeper lies a second glandular region containing large cells with long necks that extend to the external epithelial surface. Dubois (1892, 1914, 1928) believed that the photogenic tissue was made up of two kinds of secretory cells; these were the superficial ciliated cells, which possessed glandular bases (fixed secretory cells); and deeper lying glandular cells derived from clasmatocytes (migratory secretory cells). Rawitz (1891) clearly distinguished a mucous from an underlying photogenic layer. The latter, according to Förster (1914), contains pyriform cells with long necks. He believed that he could distinguish a secretory cycle in the photogenic cells. Exhausted cells at the beginning of the cycle possessed an alveolar cytoplasm; granules began to appear in the cytoplasm; the granules increased in number and stained intensely with iron haematoxylin. Those photogenic cells which were filled with granules were in the active secretory state. Transitional stages between the inactive (or depleted) cells and the active (granular) cells were rare.

An important function of the gastropod shell is to protect the body against attack by predators. If the shell of a whelk is broken away and the soft animal is then offered to a hungry cod, it is eaten readily. Many successful gastropods, however, lack an external shell as adults (although it is certain that all have evolved from shelled ancestors) and might be expected to be eaten by fish as readily as is the naked body of a broken whelk. The purpose of this paper is to describe part of an investigation into whether this is in fact true.

This is the third and concluding part of an investigation into defensive mechanisms in some British gastropods. The first part (Thompson & Slinn, 1959) dealt with a single species of opisthobranch, Pleurobranchus membranaceus, which proved able to secrete a strong acid if disturbed. The second part (Thompson, 1960 a) recorded further instances of acid secretion. The present paper describes the remainder of my work on opisthobranchs.

A number of different factors have been shown to affect the vertical migration of the zooplankton, among them changes in light intensity, temperature, salinity and the presence of food (see Russell, 1927; Hardy & Paton, 1947; Cushing, 1951; Bainbridge, 1953; Harris, 1953; Moore, 1958; Banse, 1959). The object of the present study was to find out whether in female Calanus there was any relation between vertical migration and the degree of ripeness.

When Calanus were taken by tow-nettings near the laboratory it was noticed that the percentage of adult females in the ripe condition was generally greater in hauls made close to the surface than in those from deep water. For example in the spring of 1953 a series of hauls was made near the surface in Fairlie Channel where the maximum depth is about 40 m, and at 60–80 m off Garroch Head a few miles away where the depth is 115 m. Throughout the period of examination there was a much higher percentage of ripe females in the shallow than in the deep hauls (Table 1, Fig. 1). The deep hauls show the progressive ripening of the females during the spring reaching a peak in percentage ripe which coincides with the spring diatom increase in the middle of March. It also coincides with the maximum number of eggs produced by laying females. In shallow water the sequence is not so obvious because of the high percentage of ripe females at the surface most of the time.