ZOOLOGT : MARINE INVEKTBBKATES. 78 



ant forms of life on this beach. Under the decaying seaweed of 

 the storm-wave zone, as well as farther down the beach, are al- 

 ways immense numbers of the leaping amphipod Orchestia agilis, 

 commonly called " beach-flea " or " sand flea." In color this spe- 

 cies is dark olive-green or brown, resembling the decaying seaweed 

 under which it lives. It is a very active leaper, the leaping being 

 effected by means of the posterior appendages. It burrows in the 

 sand under the seaweed, like its light colored and blue-eyed ally 

 Talorchestia, which inhabits the lower part of the beach in vast 

 numbers on outer Cape Cod and southern shores, where its bur- 

 rows usually are very abundant near the water's edge. A much 

 larger, quite closely related species, Gammams ornatus, is found 

 low down on the beach under stones, especially where fine mud 

 has taken the place of the sand. This amphipod does not leap ; 

 but when disturbed, actively wriggles away on its side, by bring- 

 ing head and tail near together and then straightening out sud- 

 denly, while bracing itself by the posterior abdominal appendages ; 

 thus repeating in a milder manner the leaping motions of its 

 more active relatives. I have seen large individuals grasp the 

 smaller ones by the middle of the back with their posterior 

 thoracic legs, and quickly scud away to hide under stones or 

 in the mud. In water these animals swim usually on their sides 

 or backs. This species is olive or dark brown in color. On 

 sandy flats and in pools left at low tide the common sand- 

 shrimp, Cranrjon vulgaris, is always abundant, either swimming, 

 resting on or buried in the sand, tail end 'down. Another abun- 

 dant small crustacean on this and other sandy shores is the 

 isopod Idolea cffca. The animal lives generally just below the 

 surface of the sand, in which position it moves about, leaving a 

 meshwork of curious " trails " all over the beach. This is seen 

 well on the lower flats of fine sand, which are covered almost 

 entirely with such markings. They can be seen even better on 

 the first beach at Swampscott. The animal is to be found usually 

 at the end of a trail, its whereabouts being marked by a little 

 lump of sand. Two species of " hermit crabs," Euparpirus hern- 

 hardus and E. !oH(iicarj)us, may be found dead occasionally on the 

 beach after storms. The former inhabits the shells of Lunatia and 

 Buccinum, while the latter, a smaller species, usually lives in shells 

 of Tritia tririttata or other small gastropods. Tiie former often 

 has its shells covered with Hydractinia, although, as already noted, 



