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.

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 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.

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.

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.

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%.

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.

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.

While collecting on the Zostera beds at Grève d’Azette, Jersey, on August 23 1937 Mr R. B. Pike found fourteen specimens of an unknown lucernarian. These Zostera beds, made famous by the work of Mr J. Hornell, are now greatly impoverished, and at extreme low tide during the spring tide period only a few scattered patches of the weed remain.

The yellowing which may occur during phosphate determinations in sea water is attributed to hydrolytic products of complex molybdenum halides.

When 1 ml. of the usual acid molybdate reagent is used per 100 ml. of water, addition of copper as recommended by Kalle reduces the development of colour in sea water samples and in distilled water standards to the same extent. The correction factor 1·12 applies to comparison by daylight in Hehner cylinders and to photometric determinations with a red filter.

When 2 ml. of reagent is used per 100 ml. of water, the factor depends on the method of comparison. With comparison by daylight in Hehner cylinders it is 1·35, whereas if a photometer with a red filter is used it is only 1·19.

The paper on the ratio of nitrogen to phosphorus in the sea (Cooper, 1937) was written before it was realized that in phosphate determinations, using two ml. of molybdate reagent per 100 ml. of water, the magnitude of the salt error correction factor is changed by the use of a spectral filter. Due to the resulting uncertainty it was felt better to use uncorrected figures for phosphate content rather than to risk a correction which might later prove to be wrong.

At Station E I,22 sea miles south-west from Plymouth, the winter maximum for phosphate, representing the stock available for plant growth in the following spring, averaged 0·67 mg.-atom/m.3 for the winters 1923–4 to 1928–9 and only 0·47 mg.-atom for 1930–1 to 1937–8. This fall in phosphate shows a close correlation with the abundance of summer-spawning young fish (Russell). Since water containing similar low phosphate appeared to occupy the English Channel in 1916 (Matthews), the inflow of warm Atlantic water in the autumn of 1921 may well have brought with it the relatively rich phosphate found in the 1920's.

The impoverishment of phosphate around 1930 runs parallel with a decrease in the easting of the residual current at the Varne lightship in the Straits of Dover (Carruthers).

On the basis of spring phosphate consumption, the years may be classified in order of productivity:

The results of a survey of the distribution of phosphates in the south-western area in April 1938 show that there were three regions exceptionally rich in phosphate. These regions appeared to be associated respectively with the outflow of the Bristol Channel, with the flow of more oceanic water across the entrance of the English Channel, and with upwelling of deeper water at the edge of the Continental Shelf.

The surface water was poorer in phosphate than the deeper water, and regions poorer in phosphate were in some cases associated with a crop of phytoplankton.

Phosphate, salinity and temperature records of waters of the North Sea and English Channel have been compared for April or May in the years 1935, 1936 and 1937, and the plankton distribution has been noted. Attention is called to the appearance of stability in certain features.

Thus, a high phosphate content was found to be associated with extremes of salinity and temperature, in similar areas in each year. The phosphate appears to be brought into the North Sea and Channel by oceanic water and by drainage from the land.

The plankton organisms were also similarly distributed in each year.

The suggestion that the enfeeblement of Zostera marina due to lack of sunshine in 1931–2 is the fundamental cause of the epidemic is not supported by the meteorological data available from 1897 onwards, or by the known extinction coefficients of the water.

The genus Bathyporeia was established by Lindström (1855, p. 59) on specimens collected in the Baltic at Wisby and Landskrona. His description is based, apart from a reference to the epimera as small and beset with hairs, on the form of the appendages. He assigned to the genus one species, pilosa, in which the segments of the body are described as smooth, the form generally rounded, the eyes black, small and somewhat reniform, and the length under three lines. He gives a detailed description and drawing of the appendages. From the description of the antennae and of the eyes it may be assumed that the specimens were females.