DISTRIBUTION OF SHORE ANIMALS. 321 



ing anemones, such as Peacliia ; burrowing Annelids, such^ 

 as Arenicola, Nerine, Glycera ; burrowing Echinoderms, 

 such as heart-urchins and Synapta ; burrowing Molluscs, 

 such as Solen, Mya, Lutraria, and so on. About the fifteen- 

 fathom line one comes to beds of clams, among which many 

 kinds of animals are to be found. Beyond this depth the 

 large seaweeds rapidly disappear, and the sea-bottom usually 

 consists of shell-gravel, sand, or mud, each region having 

 its peculiar fauna. 



If, as we have supposed throughout this book, your 

 observations are limited to those animals which can be 

 obtained without a dredge, the regions which concern you 

 are the rocks between high- and low- tide marks, the Lami- 

 narian zone, whose margin is accessible at low spring tides, 

 and the sand or mud flats to be found especially near the 

 mouths of rivers. We have named above the commonest 

 inhabitants of these regions, but if we study this fauna in 

 detail in various parts of the coast we shall find enormous 

 variation. On parts of the East Coast the spider-crab 

 Hyas araneus is extraordinarily common, on the West 

 it is comparatively rare. In the pools on the Devonshire 

 coast a pretty little prawn, Hippolyte cranchii, is very 

 abundant, but it does not occur on the East. Throughout 

 our study of the common animals we have constantly 

 encountered similar facts, and frequently emphasised the 

 differences between the fauna of the North and East and 

 that of the South and West. Those who have interested 

 themselves in the distribution of British plants know that 

 somewhat similar conditions prevail with regard to them, 

 many species being found on the West which are absent 

 from the East. In both cases this may be in part ascribed 

 to the difference of climate, the Gulf Stream making this 

 much milder on the West Coast. In both cases, however, 

 the differences cannot be wholly ascribed to differences of 

 temperature. It is not very easy to divide the British area 

 into geographical regions according to the distribution of 

 the marine animals, but the following divisions at least 

 serve to illustrate the problems involved. The German 

 naturalist Michaelsen divides the European seas into three 

 provinces: (1) the Arctic, including the seas north of a 

 line drawn from the north corner of Iceland to the Lofoten 



