272 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
like the pleural tracts; intermediate valves with a small nearly smooth 
jugum, the pleural tracts with about a dozen axially straight slender 
threads on each tract, with subequal and closer transverse threads in the 
interspaces with deep interstices; the lateral areas have two or three 
slender beaded radii on a flat substratum anteriorly, but on the posterior 
side there is a wider rib with five or six widely spaced annulations, which 
are projected backward like the teeth of a comb, beyond the margin ; 
internally the valves are whitish. Length, 12; width, 8; height, 2.3 mm. 
(Dali.) 
Type in United States National Museum, No. 58734b. Type locality, 
San Diego, California. 
Range. Known only from type locality. 
Ischnochiton ritteri Dali, 1919 
Proceedings of the United States National Museum, 55:505. 
Chiton of moderate size, brownish, darker on the prominences, with a 
rather wide girdle set with smooth oval convex whitish imbricating scales, 
the valves nearly mucronate, almost keeled; anterior valve with about 20 
flattish radii with narrower interspaces, the whole covered with a minute 
oblique decussation: internally whitish, with 16 slits, the insertion plates 
smooth, the eaves very narrow; posterior valve with a nearly central low 
mucro, the posterior tract sculptured like the anterior valve but more 
faintly, the central area punctate-retictllate; internally whitish, with 12 
slits, the sinus defined by small notches at each end, straight-edged, the 
sutural laminae narrow, elongate; intermediate valves (the first larger than 
the others) with no defined jugal area, but deeply punctate-reticulate, the 
punctations coarser toward the margins of the pleural area, lateral areas 
with three flattish radii with narrower interspaces, all covered with the 
minute reticulation; internally white with two slits at each end, one some¬ 
times obsolete; the sinus wide, concave, shallow, between two faint notches, 
the sutural laminae narrow; gill rows ambient. Length, 22; width, 15; 
height, 5 mm. (Dali.) 
Type in United States National Museum, No. 218759. Type locality, 
channel at Juneau, Alaska. 
Range. Known only from type locality. 
Ischnochiton retiporosus Carpenter, 1864 
Supplementary Report, British Association for the Advancement of Science, 649. 
Tryon and Pilsbry, Manual of Conchology, 15:75; PI. 16, figs. 47, 50-53. 
Mantle-scales very small, close, smooth. Central pattern in net-work, 
3-6 side ribs. (Carpenter.) 
[874] 
