CRUSTACEA OF THE SEASHORE 107 



terrestrial Crustacea will be mentioned in a later 

 chapter. 



There are many Shore Crabs, however, which lead 

 a more or less amphibious existence without showing 

 any marked modifications of structure as compared 

 with their more purely aquatic relatives. On our 

 own coasts, the Common Shore Crab (Carcinus 

 m&nas Plate IX.) commonly spends several hours 

 each day exposed to the air, and in an aquarium it 

 will voluntarily leave the water if the opportunity be 

 afforded it. On tropical coasts the species of Grapsus 

 and allied genera are often seen clambering with 

 great agility about exposed rocks. 



Analogous habits to those of the sand-burrowing, 

 amphibious Crabs described above are shown on a 

 small scale by the Amphipods of the family Tali- 

 tridae, known as " Sand-hoppers " or " Beach-fleas." 

 Everyone who has walked over the firm sand near 

 high-water mark on our own shores must have 

 noticed the myriads of actively hopping little crea- 

 tures disturbed at every step. The commonest 

 species of Sand-hopper on the British coasts is 

 Talitrus saltator (Fig. 39), but Orchestia gammarellus 

 is also common. Both species occur together on 

 sandy beaches or among decaying sea-weeds, and 

 are among the most important scavengers of the 

 seashore, picking clean the bones of fish or other 

 animals cast up by the tide. In this country the 

 Sand-hoppers do not, as a rule, venture far above 



