The main picture of the zonation of life between tide marks on British shores has been added to by a good deal of recent work, such as that of Colman (1932) and Evans (1947) at Plymouth, and the regional studies by Stephenson & Stephenson (1949). Of the more restricted special habitats within the tidal area there have been fewer accounts, though Colman (1940) has made a detailed survey of the faunas inhabiting intertidal seaweeds, which was later followed by Wieser (1952). Most recently there has appeared a paper by Glynne-Williams & Hobart (1952), working at Anglesey, which for the first time analysed clearly the composition and food relations of the restricted fauna living in crevices in this habitat. This part of the tidal zone forms an interesting meeting place of two faunal elements, those intertidal animals of terrestrial origin and those which are truly marine. In the summer of 1950 and 1951 the present writer had made a similar study in the Plymouth area, at Wembury and some other localities. The work was begun as part of an ecological study of the two marine pulmonates Leucophytia bidentata and Otina otis, and was later extended to take account of the other animals hidden in crevices and those living on the exposed rock surface throughout the upper half of the tidal zone.