PIERCE DE SHELES AND CHITONS 259 
Note the trough which extends from the apex to the 
margin, and which passes between the heels of the 
horseshoe-shaped muscele-sear. The shell is 51- 
mm. in length, and 13mm. in height. 
Figure 291 represents the 
shell of one of our most com- 
mon species, 7ssurélla volcano, 
Rve., the Voleano-shell. Dead 
Fig. 291 shells are abundant and attrac- 
tive, and living specimens, with yellow foot and 
red-striped mantle, may often be found on the 
rocks at low tide. The shell is about an inch in 
length and is oblong-conical in form, while the 
red stripes on its sides, running down from the 
small, oblong hole at the top, suggest streams of 
red-hot lava issuing from the crater of a voleano. 
The coloring appears plainest on dead shells; the 
live ones are darker, smoother, and less brilliant. 
Fissuridea aspera, 
EKseh., the Rough 
Keyhole-limpet, Fig- 
ure 292, (Glyphis as- 
pera). This shell is 
quite conical, with a 
small, oval hole at the Ma 
top, very different Fig. 292 
from the narrow, oblong slit of the last species. 
The edge is wrinkled, the color gray on the out- 
side, with dark, purplish rays running down from 
the apex, while the interior is white. The common 
size is rather less than that of the cut, though 
some specimens are much larger. 
