PELECYPODS 



461 



nevertheless thousands of them are destroyed by predatory star- 

 fishes, who know how to get at their victims. The restless crus- 

 taceans, ever on the outlook for a meal, 

 often nip the siphons of the rock-dwell- 

 ers, and a kind of worm sometimes 

 attacks them, and, destroying the ani- 

 mal, proceeds to occupy the empty shell 

 and burrow. 



P. costata. This species has a wide 

 geographical range, being found from Cape 

 Cod to South America, but it is not abun- 

 dant north of Hatteras. In Florida it bur- 

 rows deep in sand as well as in wood or 

 rock. On account of its white color and 

 suggestive shape and sculpture, it has re- 

 ceived the popular name of "angel's- 

 wings." It grows to a length of seven or 

 eight inches. 



JP. tnincata. This has much the same 

 range as the last, but is more commonly to 



be found in New 



England waters. It 



also burrows in any 



hard substance, or 



in mud above low- 

 water mark. It is 



especially common 



in peat-banks. 

 P. californica. 



A Californian Pho- 



las. The shell is 



about three inches in 



length, and resem- 



bles in all features 



and habits the Pholas of the east coast. Differ- 

 ences in the shell indicate that it is a distinct 



species. 



Pholas truncata. 



GENUS Zirphcea 



Z. crispata. A species of Northern range, occurring but sparingly in 

 New England, in hard clay or rocky burrows. It may be identified at once 

 by the furrow which passes from the beaks across the valves to the lower 

 edges of the shell and divides the surface of the valve into two areas. 

 The anterior area is decorated with radiating toothed ribs ; the pos- 

 terior area is smooth. This conchological feature of the genus is very 



