266 WEST AMERICAN SHELLS 
length from an inch to an inch and a half. It is 
essentially a northern species, reaching from Sitka 
to Monterey. 
Ischnochiton regularis, Cpr., the 
Regular Chiton, Figure 297. This is 
truly a regular structure, for the con- 
stant breadth is half the length, and 
the ends are semi-circles. The valves 
are sharply arched and are marked 
with very fine sculpturing. By the 
: aid of a lens the border is seen to re- 
Fig. 207 semble very fine beadwork. The color 
is olive or slaty blue, and the interior is light blue; 
length, 35 millimeters. 
Callistochiton palmulatus, Cpr., the Palm Chi- 
ton. Small, high arched, valves marked with 
raised sculpturing. The anterior valve has eleven 
ribs, and the posterior valve has seven very strong 
ones, bifurcated behind. Its color is dark brown, 
and its length is 11mm. It is found at Monterey 
and Santa Barbara. The variety mirabilis, Pils., 
has the last valve enormously thickened. The in- 
terior is bluish white. From San Diego. 
Callistochiton crassicostatus, Pilsbry, the Thick- 
ribbed Chiton, has an elevated, oblong shell, the 
surface lusterless, green or brown. The front 
valve has seven very strong ribs; the posterior 
valve is also elevated, the hinged area not higher 
than the area in front of it. The interior is bluish 
white; length, 22mm.; found at Monterey. 
