K0.2283. NEW PACIFIC COAST CHITONS— DALL. 505 



ISCHNOCHITON RITTERI, new species. 



Chiton of moderate size, brownish, darker on the prominences, 

 witli a rather wide girdle set with smooth oval convex whitish im- 

 bricating 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-reticulate ; internally whitish, with 12 slits, the sinus defined 

 by small notches at each end, straight edged, the sutural lamina? nar- 

 row, elongate; intermediate valves (the first larger than the others) 

 with no defined jugal area, but deeply punctate-reticulate, the puncta- 

 tions coarser toward the margins of the pleural area, lateral areas 

 with three flattish radii Avith narrower interspaces, all covered with 

 the minute reticulation; internally white with two slits at each end, 

 one sometimes obsolete; the sinus wide, concave, shallow, betv/een 

 tw"0 faint notches, the sutural laminae narrow ; gill rows ambient. 

 Length, 22; width, 15; height, 5 mm. 



Habitat. — Channel at Juneau, Alaska, Harriman Alaska Expedi- 

 tion, collected by Professor W. E. Bitter. Cat. No. 218759, U.S.N.M. 



? ISCHNOCHITON EXANTHEMATUS, new species. 



Chiton of moderate size, of dark yellowish brown color, lighter on 

 the jugum, the girdle covered with densely set short spinules whose 

 ends form a minute tessellation on the surface; anterior valve less 

 than semicircular, sculptured with concentric incremental lines and 

 over the entire surface with very minute granular pustules ; internally 

 with about 18 slits, w^ith very short smooth insertion plates and rather 

 spongy eaves; the posterior valve has similar sculpture on the poste- 

 rior area, the low mucro at the anterior fourth of the valve and the 

 narrow central area merely transversely striated; internally there are 

 14 slits, the insertion plates faintly striated in part, the sutural 

 laminae very narrow, the sinus hardly perceptible, the color white; 

 intermediate valves hardly mucronate, the jugal area smooth except 

 for microscopic punctations, the pleural tracts with seven or eight 

 axial thread-like lines w^ith Avider interspaces, minutely punctate, 

 on each side; the lateral areas feebly concentrically ribbed and granu- 

 lose like the end valves; internally with one or two slits indifferently 

 on the same valve, the sinus wide, very shallow and ill-defined, the 

 sutural laminae narrow, arcuate. Length, 10; width, T; height, 

 4 mm. 



Habitat. — Straits of Magellan in 61 fathoms, sand, bottom tem- 

 perature 48°, United States Fish Commission steamer Albatross. 

 Cat. No. 96226, U.S.N.M. 



