The faunal analysis of forty-eight samples taken with a coarse tow-net across the intertidal waters of Kames Bay during 1936 shows that the night migrant crustacean population falls into two well-marked groups: (a) those species which live in the intertidal sand and perform simple vertical migrations at night-time into the intertidal waters, and (b) those which are carried in by the tide into the intertidal area from various habitats which lie beyond the low-water mark of spring tides. In the former group the species of the genera Bathyporeia and Pontocrates are dominant and they retain their zonation as migrants, the population consisting of individuals in all stages of maturity. This is in sharp contrast to the latter group, typified by Gammarus locusta and Idotea viridis, which occur over the whole tidal range with a population in which the young immature stages are dominant. The Haustoriids Urothoë brevicornis and Haustorius arenarius occur as inhabitants of the sand, the former appearing occasionally in the tow-net samples and the latter absent from them. The Cirolanid Eurydice pulchra performs both day and night migration for the purposes of feeding.

Discussion of the results indicates the lines along which further investigations may be carried out.