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. 
P. truncata. 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- Pholas costata. 
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 Zirphea 
Z. crispata. A species of Northern rarlge, 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 
