224 WEST AMERICAN SHELEES 
and triangular. The species assumes many forms, 
and is sometimes almost white and free from 
spines. Its home is to the south of Monterey Bay. 
Calyptrea mamillaris, Brod., the Chinese Hat, 
has a white shell, of a low conical shape, running 
up to a point, while inside there is a twisted deck, 
the whole thing being the size of a medium button. 
Northern, though occasionally found south. 
There is a large group of shells whose shells are 
somewhat turtle-shaped, with a floor built over a 
part of the lower surface. When turned over, they 
somewhat resemble a Chinese slipper, with a place 
for the toes of the wearer’s foot. So apparent is 
the resemblance that they are universally called 
Shpper-shells. 
Crepidula adunca, Sby., the 
Hooked Slipper-shell, Figure 244, is 
perhaps the commonest species. The 
apex is strongly recurved, suggest- Higwet 
ing the name, and the surface is brown, though 
the deck is white. Living specimens may often be 
found growing upon other shells, and sometimes 
they are piled one upon another three deep. Young 
shells often have the apical hook quite pointed. 
Crepidula onyx, var. rugosa, Nutt., the Onyx 
Slipper-shell, somewhat resembles the last, but in 
favorable locations it grows to a much greater 
size. The surface is somewhat roughened or 
shaggy, and the apex is on the very edge of the 
shell. Beautiful specimens are found in San 
Pedro Bay, some of them measuring 55mm. in 
length, the inside being colored a dark, glossy 
