OTHERS BIVALY E MOLLUSKS 103 
Pholadidea parva, Tryon, the Little Piddock, is 
a very small species, which some consider as a 
small variety of the last. It burrows into Halio- 
tis shells. 
Pholadidea ovoidea, Gld., the Oval Piddock, is 
a small, oval form, resembling in shape a small Z. 
erispata, whose forward end is filled out with 
eurved shell. 
Pholadidea darwinii, Sby., Darwin’s Piddock, 
(Netastomella d.), is a little borer found in rocks. 
The front of the shell is open and circular, while 
the latter part is prolonged into a narrow, flat- 
tened tube, shaped lke a duck’s bill. The shell is 
marked with striw, and is divided into two parts 
by a sudden constriction. Whitish; about half an 
inch long. 
Figure 91 gives 
a good idea of the 
shell of the Rough 
Piddock, Zirphaéa 
erispata, Innn. 
This fine borer is 
able to force a tun- 
nel into the hard- 
est of blue clay, doubtless by means of its sharp 
rasp. There is no accessory plate over the hinge- 
area in this species, but it is protected by a mem- 
brane, and in front of the umbones the valves are 
reflexed. The shell is thin, white, and very hard, 
and the length is from two to four inches. ‘This 
species is widely distributed, being found in both 
great oceans. 
