270 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
mucro as in I. magdalenensis; anterior valve with about 8, posterior about 
10 slits, intermediate valves with 2 slits; sinus wide, entire; pleural laminae 
wide, short; long., in the dry state, 36; lat., 15; alt., 5 mm. (Dali.) 
Type in United States National Museum, No. 109043. Type locality, 
San Martin Island, Lower California. 
Range. San Pedro, California, to Gulf of California. 
Ischnochiton conspicuus (Carpenter) Pilsbry, 1892 
Tryon and Pilsbry, Manual of Conchology, 14:63; PI. 15, figs. 91-96. 
Shell large, elongated, moderately elevated; green (or rarely earthy- 
brown), but where eroded at the beaks it is pink. Interior pink, with a 
blue spot at the jugal sinus. Lateral area much raised, having acute radi¬ 
ating riblets or striae; central area apparently smooth, but microscopically 
granulated, sometimes having some faint longitudinal striae at the jugum. 
Front slope of the anterior valve concave; girdle densely beset with short 
bristles, giving it a velvety aspect The entire surface is very densely, 
microscopically granulated, where not eroded. The lateral areas have fine 
acute radii and often the black edge of each valve is crenulated by oblique, 
sharp, little folds. The color is often varied by darker little flames on the 
central areas. The posterior valve is large and depressed. The sutural 
plates are large, the sinus deep and angular. Insertion plates having in 
anterior valve 9, central valves 2 or 3, posterior valve 10 slits. Teeth 
sharp and thin in posterior and central valves, but blunt and bi- or tri- 
lobed in anterior valve. Eaves wide, solid, light blue-green colored. Length, 
82; breadth, 36 mm. Length, 89; breadth, 41 mm. 
Type in Academy of Natural Sciences, Philadelphia, No. 35704. Type 
locality, San Diego, California. 
Range. Monterey, California, to Gulf of California. 
Ischnochiton marmoratus Dali, 1919 
Proceedings of the United States National Museum, 55:503. 
Chiton small, elegantly marbled with white, gray, and brown, with a 
velvety girdle covered with mottled gray, white, and brown densely set 
spinules; anterior valve with about 12 radial rows of prominent pustules, 
the rows sometimes bifid, and the ground microscopically decussate; slits 
8-10; posterior valves smaller, with 8-9 slits, the mucro slightly behind 
the center with a peripheral irregularly double row of pustules while the 
central area is coarsely axially reticulate; intermediate valves with one 
slit, hardly mucronate, the jugal and pleural tracts axially sculptured with 
beaded threads finer on the jugum; lateral areas with two or three radial 
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