96 WEST AMERICAN SHELES 
thin, whitish, covered with a gray, wrinkled epi- 
dermis. The cartilage pit is large, and triangular 
in shape. The pallial sinus reaches nearly to the 
middle of the shell. These great Dish-shells some- 
times reach a length of over five inches, and can 
hardly be mistaken for any other species, except 
the next. 
Spisula hemphilla, Dall, Hemphill’s Mactra, is 
a rare species occurring in San Pedro Bay and 
San Diego. It resembles the last species, but 
grows even larger, a specimen before me measur- 
ing six inches in length. The white shell is covered 
with a brown periostracum, which in young shells 
is prettily lined, and almost glossy, while at the 
posterior end it is decidedly ridged and wrinkled. 
The front end of this shell is narrower than that of 
+ From The Nautilus, vol. vii, p. 138. 
