MARINE ARTHROPODS 289 



moving bed still further serve to obscure the nature of the living 

 mass below a mass that is always in danger of becoming the prey 

 of the fishes which inhabit deep water. It is probable, therefore, 

 that this association is one that is beneficial to both sides as far as 

 the animal life is concerned, the lower species serving to disguise 

 the true nature of the crab, thus protecting it from its numerous 

 enemies, while they in return are conveyed, carriage paid, to the 

 feeding-grounds, where they can freely partake of the fragments 

 that become diffused in the surrounding water. 



Our illustration on p. 288 shows three species of spider crabs, 

 all of which are common on parts of our shores. The Scorpion 

 Spider Crab (Inachus dorsetensis) derive* its specific name from 

 the fact that it was first found off the coast of Dorset ; but it is 

 abundant off many of our shores, both in the south and north, and 

 may frequently be seen entangled among the fishermen's nets. It 

 may be distinguished from other and similar species by the four 

 spines arranged in a line across the front portion of the carapace, 

 and the five large, pointed tubercles behind them. This species is 

 undoubtedly a favourite food of the cod, for several specimens may 

 often be taken from the stomach of a single fish. 



The next species The Slender-beaked Spider Crab (Steno- 

 rhynclms tenuirostris) is seldom missing from the dredgings 

 hauled in off the south-west coast, and is fairly common in other 

 parts. Its legs are extremely slender, and bear spines on the inner 

 side, and its body, where free from the incrustations so often 

 covering the carapace of spider crabs, is of a fresh pink colour. 



The other one shown in the same illustration is Arctopsis 

 lanata, sometimes known as Gibb's Crab, the carapace of which 

 is pointed behind, bears a large pointed tubercle on each side, and 

 is completely covered with a thick clothing of stiff hairs. It is also 

 common on many parts of our coasts, more especially the coasts of 

 Devon and Cornwall. 



Closely allied to the last-named, and belonging to the same 

 family, is the well-known Thornback Crab (Maia Squinado), also 

 a very common crab, of which we give a separate illustration. 



The tribe Catametopa does not contain many British species, the 

 principal being the Pea Crabs ; the Floating Crab, which is occasion- 

 ally washed on the south-west coast; and the beautiful Angular 

 Crab. In these the front of the carapace is turned downwards a 

 feature that has suggested the name of the tribe. 



The pea crabs are all small, and they are parasites, living 



u 



