226 WEST AMERICAN SHELLS 
are occasionally found in San Pedro Bay, usually 
clinging to the outside of a large Pecten. In shape 
it resembles a very large Crepidula adunea, but 
there is no deck inside the shell. Externally it has 
a brown epidermis, somewhat shaggy, while within 
it is beautifully white. Its length is 40 millimeters. 
There is a series of white shells, dead specimens 
of which are abundant, which pre- 
sent a rather puzzling aspect, and 
which vary greatly in outward ap- 
pearance. They are not spiral, but 
appear like hollow cones, more or 
less flattened, with the apex to one side of the 
center. Some of them are singularly like a horse’s 
hoof in shape, while others resemble Figure 246, 
which represents the species named Amalthea an- 
tiquata, Linn, the Ancient Hoof-shell, (Hipponyx 
antiquatus). Some specimens are less flattened 
than the picture, but all are more or less rough 
and sealy externally, while within you can see the 
muscle-sear in the shape of a horse-shoe. The 
eolor is white, and the diameter is about half an 
inch. Occasionally living specimens may be found 
with a shelly base attached to a rock, secreted by 
the animal’s foot. 
Amalthea cranioides, Cpr., the Flat Hoof-shell, 
resembles the last species, but has a still flatter 
shell, with the apex somewhat near the center in- 
stead of at one side. 
Amalthea tumens, Cpr., the Seulptured Hoof- 
shell, (Hipponyx tumens), has a much more regu- 
lar shell than either of the others. The apex is 
Fig. 246 
