By examination of samples of Purpura lapillus from the whole of their European range, it appears that the species can exhibit quite as wide variation within a relatively small region such as that studied in the Dorset-Devon-Cornwall area, as it can over its whole geographic range. Population samples were taken from seventy-six localities, mostly in the south-west of England, and covering a wide range of environmental conditions, and the variations in these shells were studied in relation to two primary environmental factors, degree of exposure to wave-action and diet.

Chthamalus stellatus is a littoral barnacle very similar in habitat and general ecological relations to another littoral barnacle, Balanus balanoides. In those localities where both species flourish they compete considerably for space, and also possibly for food. The fact that B. balanoides settles sooner after the winter storms than does Chthamalus probably favours the former.Chthamalus is characteristically a southern species and Balanus balanoides a northern one, but the north and south ranges of the two species overlap in the British Isles and in France. The determining factor is presumably temperature.Chthamalus is an Atlantic species, and Balanus balanoides is more characteristically a North Sea species. The essential factor in Atlantic water remains unknown, although in respect of a need for Atlantic water Chthamalus resembles Sagitta elegans and intertidal Echinus esculent.

The macrofauna of the intertidal mud-flats of the River Tamar have been investigated. Quantitative samples were taken by sieving the mud through a o·8 mm. sieve. Traverses of series of stations were worked at successive intervals up the river, and the tidal level of each station ascertained.The characteristic species which inhabit the mud-flats are listed and the data secured regarding (1) population density, (2) up-river penetration, and (3) vertical distribution, are summarized and related to previous information on these points.While some species are more or less uniformly distributed intertidally, others show marked zonation, with maxima in one part or another of the intertidal zone. Marine species which penetrate into the estuary tend to show the same intertidal distribution as in marine habitats. All five of the more strictly estuarine species are concentrated in the upper tidal levels.In considering the limiting factors which cause a decrease of population at lower tidal levels, emphasis is placed on the probable importance of the increase in strength of water currents towards low water.

A PRELIMINARY survey of the area with regard to the distribution of the total nitrogen and phosphate content of the muds was described in a previous paper (Moore,5). A number of stations were worked, and these were further examined for nature and distribution of particles, water content, and density, and as a result of this survey certain stations were chosen as suitable for more extensive work. At the same time it became evident that the layers in which the greatest and most important changes were taking place were those within a few centimetres of the surface, and these were therefore studied most intensively.Among these stations many show very irregular deposition, owing to tidal currents or other causes. At some, conditions appear to be comparatively'stable, and a series of these was chosen to illustrate the four chief types of mud found in this area, which are as follows :-Deep Water Type. This is found in the deepest channels where there is little or no tidal action, a slow rate of sedimentation and very little influence from the land, e.g. Station 7, no metres; St. 7b, 166 metres; St. 23, 73 metres.Mid-Loch Type. This is a shallower water type than the preceding, usually in a depth of 45 to 75 metres. There is little tidal action and the small amount of matter received from streams is of very fine grade. Deposition is more rapid, and the mud tends to be softer than in the previous type, e.g. Station 8b, 37 m.; St. 9, 37 m., Kyles of Eute; St. n, 73 m., Loch Striven; St. 13, 73 m., Loch Goil; St. 13a, 82 m. ; St. 15,58 m.; St. 15a, 64 m., Loch Long; St. 16a, 26 m., Holy Loch.