452 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Genus ISCHNOCHITON Gray, 1847. 
Valves external, with sharp, slit insertion plates, the teeth not buttressed. Eaves generally solid; 
girdle covered with imbricating scales, flat or convex, smooth or striated. 
Subgenus Stenoplax Carpenter, 1878. 
Ischnochiton limaciformis Sowerby. 
Chiton limaciformis Sowerby, P. Z. S., 1832, p. 26. 
Ischnochiton limaciformis Pilsbry, Man., xiv,p. 57, pl.xvi, figs. 9-16, 1892. 
Shell elongated, narrow, elevated, buff gray, or greenish, marbled indistinctly with darker 
color, occasionally blotched with red, longitudinally costellate but not granose; girdle scales minute; 
sculpture of the central areas consisting of fine, smooth longitudinal riblets; these continue on the lateral 
areas, becoming broader and flat, and are waved on the slope between the two areas. End valves 
sculptured with close, flattened, concentric ridges, which are somewhat wavy. 
Length, 35; breadth, 12 mm. 
Ponce Reefs, Porto Rico. 
Ischnochiton purpurascens C. B. Adams. 
Chiton purpurascens C. B. Adams, Proc. Bost. Soc. Nat. Hist., 1845, p. 9. 
Ischnochiton purpurascens Pilsbry, Man., xiv, p. 58, pi. xvii, figs. 23, 24, 1892. 
Eastern Porto Rico (Gundlach). 
Ischnochiton floridanus Pilsbry. 
Ischnochiton floridanus Pilsbry, Man., xiv, p. 58, pi. xvii, figs. 19-22, 1892. 
Shell elongated, narrow, elevated, the valves roundly arched, not carinated; lateral areas raised, 
longitudinally costellate, the riblets cut into granules by radiating, impressed lines over the whole 
area or the forward part of it. End valves cut into granules; central areas longitudinally ribbed; 
posterior valve large, rather depressed, the mucro slightly posterior; girdle delicately marbled with 
bluish and gray, densely covered with rounded, solid, striated scales. Color whitish or pale green, 
variously mottled with olive, blackish, or gray. 
Length, 35; breadth, 11.5 mm. 
Ensenada Honda, Culebra, one small specimen. 
Subgenus Trachydekmon Carpenter, 1863. 
Ischnochiton liozonis, n. sp. 
Animal small, girdle nearly smooth, reddish brown; valves dark red, more or less flecked with 
white, or white and gray; surface of the valves nearly smooth, minutely granulose, the granules more 
evident on the lateral areas which are slightly raised; anterior valve small, with ten slits, above with 
some obscure radiating ridges; middle valves with moderately prominent mucro, wide dorsal angle, no 
radial sculpture, the insertion plates with one slit, interior of valve pinkish white, sinus wide, the 
valve callus forming a strong bow-shaped ridge; posterior with a moderately elevated mucro, narrower 
sinus, ten or eleven slits, the tegmentum much the shape of a watermelon seed. Gills median. 
Length, about 10; width, about 7 mm. 
Ensenada Honda, Culebra; Porto Rico, two specimens. 
Subgenus Ischnochiton Gray. 
Ischnochiton striolatus Gray. 
Chiton striolatus Gray, Spic. Zool., p. 6, 1828. 
Chiton striolatus Reeve, Conch. Icon., Chiton, pi. xxn, fig. 144, 1847. 
Shell oblong, the back distinctly or faintly keeled, side slopes convex. Surface apparently 
smooth, the lateral areas moderately distinct, somewhat raised, sculptured longitudinally with narrow 
zigzag grooves; central areas having excessively fine quincuncial granulation; end valves with 
concentric, zigzag grooves and minute granulation; girdle whitish, clouded blue with orange flecks 
generally, and densely covered with striate scales. Color variable, usually olive green, slaty or 
cream-colored, more or less mottled. 
Length, 14; breadth, 8 mm. 
Arroyo; Ponce, Porto Rico; Ensenada Honda, Culebra. 
