298 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Callistochiton chthonius Dali, 1919 
Proceedings of the United States National Museum, 55:511. 
Chiton of moderate size and dark reddish-brown color, including the 
girdle which exhibits small lozenge-shaped imbricating scales uniform over 
the surface; anterior valve with 11 subcarinate radial ribs, the two pos¬ 
terior tending to bifurcate, and nine slits; the ribs are hardly nodulous, 
and in the type the interspaces are reticulated only on the left side of the 
axis; posterior valve with 13 slits, nine nodulous riblets, the mucro sub¬ 
central, the central area axially threaded with a median smooth keel; inter¬ 
mediate valves with a smooth narrow keel at the jugum, the pleural tracts 
with a strong rectangular reticulation; the lateral areas with two strong 
keeled ribs, the posterior rib bifurcate for most of its length and the 
distal ends sometimes divided; these ribs are more or less nodulous, den- 
ticulating the posterior edge of the valve; the interspace between the main 
ribs is deep and angular; the insertion plates have a single slit; the interior 
of the posterior valve dark green, of the other valves greenish-white; the 
jugal sinus is very shallow, straight-edged and wide, the sutural laminae 
rather narrow. Length, 21.5; width, 10; height, 5 mm. (Dali.) 
Type in United States National Museum, No. 109488. Type locality, 
San Pedro, California. 
Range. Known only from the type locality. 
Callistochiton cyanosus Dali, 1919 
Proceedings of the United States National Museum , 55:511. 
Chiton of moderate size, rounded back, and rather low dorsum, the 
color pale blue with interrupted bands of straw-color, the girdle armature 
as usual, but rather finer and pale in color; anterior valve with 11 keeled 
ribs, a slit to 9 of them; these ribs are crossed by fine concentric threads 
with about equal, not punctate, interspaces; posterior valve low, with sub¬ 
central mucro similarly sculptured, the central area rather larger than the 
ribbed portion with 10 or 11 prominent axial threads on each side, the 
interspaces crossed by similar threads, making a conspicuous reticulation; 
in the posterior portion are 8 carinate ribs each with a slit; the intermediate 
valves with one slit on each end, the lateral areas bounded by 2 strong 
keeled ribs crossed by small equal threads, not punctate in the interspaces, 
denticulating the posterior edge of the area; jugal areas showing a narrow 
triangular smooth space, on each side of which are 15 or more strong 
straight axial threads, the subequal interspaces reticulated by smaller 
threads and the interstices deep; interior bluish-white with a wide straight- 
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