240 WEST AMERICAN SHELLS 
the surface, or, when the weather is too rough, it 
sinks to more quiet abodes. 
Quite similar in 
general form and 
habits is the Chan- 
neled Top-shell, Cal- 
liostoma  canalicula- 
tum, Mart., Figure 
266. Its shape “is 
strictly conical, and 
the flattened whorls 
are girdled with deep, 
spiral channels, which 
le between raised 
Fig. 266, x 5 (4) ridges. The surface 
is ash-colored, though the shell is rainbow-tinted 
within. The thin exterior layers may very readily 
be removed by a weak acid, if one wishes to exam- 
ine the deeper structure of the shell. 
Figure 267 presents to us another 
shell, Calliostoma costatum, Mart., the , 
Blue Top-shell. This species is smal- €& 
ler than either of the preceding mem- * 
bers of the genus, and lives nearer the 
shore. Hence we would naturally Fig. 267 
expect to find that it had a thicker and stronger 
shell than the others, and in this we are not dis- 
appointed. It has four rounded whorls, marked 
with fine spiral ridges. The thin, reddish brown 
outer coat is readily removed, showing the blue 
pearly layer underneath. 
I have found very fine living specimens hanging 
