CLASS GASTROPODA 
293 
narrow longitudinal cords, parallel at the dorsal ridge except on the second 
valve in which they diverge forward; the interstices wider than the cords, 
and finely latticed across. Anterior valve having 9 stout radiating ribs, 
strongly granose, and with the exception of the two outer ones, they are 
generally not bifid. Posterior valve much higher than the anterior, the 
mucro somewhat in front of the middle, the area behind it enormously 
developed, elevated and convex, sculptured with 4, 5, or 6 primary stout 
ribs, each of which splits into two; the two outer ribs are broader, and 
split into several riblets. Interior bluish-white; sutural-laminae slightly 
connected across the squarish sinus. Anterior valve having 9, central 1, 
posterior valve 22 slits; teeth short, somewhat roughened. Eaves broad, 
calloused. Girdle narrow, thin, covered with very densely imbricating, 
minute, deeply striated scales. Length, 16; breadth, 7 mm. (Pilsbry.) 
Type in Philadelphia Academy of Sciences. Type locality, San Diego, 
California. 
Range. Known only from the type locality. 
Callistochiton crassicostatus Pilsbry, 1892 
Tryon and Pilsbry, Manual of Conchology, 14:264; PI. 58, figs. 1-6. 
Shell oblong, elevated, the dorsal ridge very obsoletely angular, side- 
slopes arched. Surface lusterless, green or brown. Valves not beaked, the 
lateral areas extremely prominent, unevenly granulated, the concentric 
riblets being cut by one or several radiating grooves. Central areas having 
strong longitudinal bars, converging A-like on the ridge (even on the sec¬ 
ond valve), the intervals very closely and finely latticed across. Anterior 
valve having seven very strong ribs, each divided by a shallow median 
groove. Posterior valve elevated, having the mucro directly over the pos¬ 
terior edge, the hinder area not higher than the area in front of it; pos¬ 
terior slope vertical, convex, sculptured with five very strong, deeply 
separated ribs, which are granose above, and subdivide into several riblets 
each toward the lower margin. Interior bluish-white; sutural-plates 
slightly connected across the rounded sinus. Anterior valve having 9, 
central valves 1, posterior valve 13-20 slits; teeth short, rather sharp and 
smooth, hardly projecting below the eaves, thickened along the slits out¬ 
side; eaves broad, solid. Girdle narrow, thin, covered with excessively 
minute, closely imbricating, striated scales. Length, 22; breadth, 9 mm. 
(Tryon and Pilsbry, Manual of Conchology.) 
Type in Philadelphia Academy of Sciences. Type locality, Monterey, 
California. 
Range. Forrester Island, Alaska, to San Diego, California. 
[895 ] 
