The work of which an account is here given was largely carried out from the autumn of 1937 to the spring of 1940, when it was interrupted by the war. In taking it up again (in July 1945) while, facilities for field work are still limited, the author feels it useful to publish results as they stand and indicate where further work is considered advisable.

In examinations of the free-swimming bottom fauna of the Tamar and other estuaries, attention was inevitably drawn to the populations of Gammarus species, which make up the greater bulk of it. Before quantitative observations were planned, some interesting points came to light with regard to the qualitative composition of populations. This aspect lent itself more readily to study and, though byno means a new field for exploration, soon proved worth examining ingreater detail than previous workers had attempted.

The broad fact of a replacement of one Gammarus species by another in passing up an estuary was well enough known, though exact knowledge for the British Isles only starts from the time when G. zaddachi Sexton was recognized as a regular member of the upper estuarine fauna of the Tay (Bassindale, 1933; Alexander, Southgate & Bassindale, 1935) and of the Deben (Serventy, 1935). This species proved to be the main brackish-water species overlapping with the marine G. locusta (L.) near the seaward end, and with the fresh-water G. pulex (L.) at the river end (or ‘head’) of the estuary. The status in estuaries of two other brackish-water species, G. duebeni Lillj. and G. chevreuxi Sexton, remained obscure.

1039 flounders were marked with numbered vulcanite disks in the estuaries of the Tamar and Lynher.

148 flounders were recaptured and of these seven fish were recovered a second time after one recovery and release, and one fish was recaptured on three occasions after two previous recoveries and releases.

Only two fish were recovered at a distance from Plymouth. Both had moved eastward, up the English Channel.

There was little or no growth in the winter months.

Individual growth rates were found to vary greatly.

The flounders living in the last reach of the Tamar near Saltash tended to remain in one limited area during the winter months, save for a drift down-stream of some of the larger fish. In the spring there was an upstream movement of the smaller, immature fish.

Flounders which had gone down to the sea to spawn might return to the river in which they were marked, or to the other river of the two which join to form the Hamoaze, or they might move right away from the area where they were marked.

The distributions of mackerel eggs and young stages, pilchard eggs, the siphonophore Muggiaea atlantica and the chaetognaths Sagitta elegans, S. setosa, S. serratodentata and 5. lyra in the Celtic Sea in March 1939, April, May-June 1937, 1938 and 1939 and July 1937 and 1938 are described, together with notes on the hydrological conditions in April 1937, 1938 and 1939, May-June 1939 and July 1938.

Mackerel spawning started in mid-March, rapidly reached a maximum in mid-April, declined gradually through May and June and was very slight at the end of July.

The changes in intensity of spawning are accompanied by a continuous shift eastward and slightly northward of the locus of spawning. In March spawning occurred in a small area at the western edge of the Continental Shelf only. In mid-April it was spread over the greater part of the Celtic Sea, with the main activity concentrated in two centres—to the south of Ireland and to the west of the mouth of the English Channel. By May-June it had shifted farther to the east and occupied the central area of the Celtic Sea. In July there was no spawning to the westward of the Scilly Isles.

The spawning area of the mackerel appears to be confined to the shallow waters over the Continental Shelf.

No mackerel young stages were found in March. Small numbers occurred in April (maximum 174). They were abundant in May-June (maximum 8239), and very scarce in July (maximum 20).

The distribution of young stages closely follows the movement of spawning during the season.

The Lernaeopodidae are a highly specialized group of parasitic Copepoda presumably derived from a Caligoid stem, and some clue to their systematic position should be found in their development. Some stages are known in ten genera, but it is only in Achtheres, Salmincola, and Clavella that the whole, or nearly the whole, series of stages has been described. There is a very strong tendencyto suppress the nauplius as a free stage though, when so suppressed, there may be moults corresponding to nauplius and metanauplius (Zandt, 1935). In some species there is certainly a free nauplius, but it probably moults into the copepodid in a very short time.

I should like to place on record the circumstances under which I saw for the first time that the male cells of the Dictyota family were not non-motile spermatia but ciliated motile antherozoids.

The occurrence in the summer of 1945 of a swarm of Physalia physalis L. off the south-west coast of the British Isles has initiated a survey into records of its appearance on the Atlantic coasts of Europe during the past 100 years. Unpublished records for 1912, 1913, 1934 and 1935 were discovered and are listed with those already known. The 1945 strandings are considered in detail in conjunction with meteorological data for the period involved. It is concluded that winds, rather than water movements, are the main factor in transporting the swarms towards the British Isles and it is considered likely that the swarms come from the Azores-mid-Atlantic region rather than from the Canaries-Gibraltar district.

Associated with the Physalia were Lepas fascicularis and L. pectinata, some Velella, a few turtles (Caretta caretta), and possibly an Opah fish (Lampris luna), all of them, with some reservation respecting the last-named, surface organisms that would come under the same meteorological influences as the Physalia.

A living specimen of Physalia gave an opportunity to observe the method of feeding of which few previous first-hand accounts exist. The capture of the prey by the dactylozooids and its subsequent digestion by the gastrozooids is illustrated by photographs from life and is described in some detail. It is suggested that the rolling of the pneumatophore from side to side, dipping the crest in the water, is a calm-weather habit directed to keeping moist the upper surface exposed to the air.

The work includes an investigation of the intertidal distribution of several species previously studied in Cardigan Bay. Twelve localities in the neighbourhood of Plymouth were selected for study, showing a range from conditions of extreme exposure to surf action to conditions of maximum shelter. The main features of rock configuration and surf action at the different localities are briefly described.

The method of investigation is described, and results obtained for the zonation of the fucoids on Church Reef are compared with the results of Colman (1933). It concluded that the method of survey adopted in the present work yields results of a high degree of accuracy.

The horizontal and vertical distributions of the flora are described and related to the intensity of surf action. This is followed by a discussion of the effects of wave intensity and wave frequency on the distribution of algae in general. The importance of the frequency of wave shock in the mid-tidal region of the shore, and its influence on algal colonization, is stressed. An attempt is made to arrange the algae studied in order of decreasing tolerance of surf.

The distribution of the selected species of animals at the different localities is described; and a discussion follows on the effect of wave action as a presence or absence factor in horizontal distribution, and as a modifying factor on vertical zonation. The effect of surf on the size of individuals of certain species is also commented upon.

The relation of the plant and animal species to different percentage exposures to the air at different shore levels is discussed.

As is well known, the species Gammarus zaddachi, established by E. W. Sexton in 1912 on material from European brackish and fresh-water localities, has caused great confusion among zoologists, as the characteristics distinguishing it from various related species, particularly Gammarus locusta, G. duebeni and G. pulex, have been very frequently disregarded. This confusion still persists to-day—that is amply shown by the material received for the present investigations from various museums.

Pycnoclavella aurilucens was recorded and briefly described by Garstang in 1891 from a limited locality in the Plymouth area, and has not been found with certainty of identification from any other region. There has been a tendency to subordinate it as a species of Clavelina, but the dissimilarities are greater even than the original description implies and this procedure is not justified. The genus is accordingly retained, and a more detailed account of the colony, with the first description of the tadpole larva and process of budding, is presented.