36 
LORQUINIA 
laris), and in this case the shell shows ribs similar to the ribs of the 
Pecten. Crepidiila are sometimes found on the very rough surface of 
Astrea iindoas, such crepidula being very irregular in shape and 
usually small. Still another and quite distinct form is caused by the 
growth of one upon another, sometimes as many as 10 or 12 forming 
a cluster. These are deep and narrow, and have one edge much 
longer than the other. 
The foot, which nearly fills the large opening in the shell, is not 
used for moving about because the shell grows to fit one particular 
spot on the base, whatever it may be, and there the crepidula clings 
with surprising tenacity. Should it fall from its perch or base, its 
open shell leaves it an easy prey to the crabs and fishes. 
The color of the deck or septum is always white and the rest of 
the interior of the shell is chocolate or dark brown in color. These 
shells are common along our coast. 
Another Crepidula which is only slightly less variable in form 
than C. onyx is C. cxcavata Brod. The distinguishing characters of 
this species are, first, the evenly curved deck, which extends along the 
shell at both sides ; second, the position of the apex, which is dis- 
tinctly raised from the edge of the shell ; and third, the pocket or 
excavated space at the posterior end of the deck. 
The outline and depth of the shell vary as in C. onyx, several va- 
rieties having been named. This species usually lives below the low 
tide mark and does not appear to be as common as C. onyx. 
Crepidula dorsata Brod. is a common form that is found on the 
rocks of the breakwater at San Pedro at low tide. This little fellow 
is normally circular and rather flat. The deck is nearly triangular 
and has two sides free. The shell is white streaked with light brown, 
and the deck is white. The outside of the shell is frequently covered 
with nullipore. 
Crepidula crepidula Lam. is the name of the little white slipper 
shell that we find living inside of dead univalves. When very small 
its shell is oval and flat; but, as it grows, it becomes long, narrow and 
bent to fit the concave surface on which it rests. This gives it the 
appearance, when taken from its base, of having grown inside out, 
the deck being on the convex side of the shell. With a hermit crab 
tliis little crepidula frequently shares the shell in which he is growing. 
E. P. CHACE, 
Eos Angeles, Cal. 
