504 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.55. 



ISCHNOCHITON BRUNNEUS, new epecies. 



Chiton of moderate size, flattish, of a yellowish brown with a few 

 black flecks on the girdle, which is armed with smooth oval slightly- 

 imbricating scales; anterior valve with 11, posterior with 14, inter- 

 mediate with single slits ; anterior valve with about 16 beaded radial 

 ribs sometimes bifurcate, the posterior margin denticulate, the inter- 

 spaces microscopically reticulate; posterior valve flattish, the mucro 

 slightly behind the center, with about 14 sometimes bifid rows of pus- 

 tules with the same reticulate ground ; the central area is sculptured 

 like the pleural tracts of the intermediate valves; the latter valves 

 have a nearly smooth mucro and feeble dorsal carination ; the pleural 

 tracts have 8 or 10 axial undulated tlireads on each side, beneath which 

 are more closely set coarser transverse threads with deeply punctate 

 interstices; the lateral areas have three or four radial ribs, the 

 posterior annulate, denticulating the posterior margin, the others 

 beaded, the substratum everywhere with the minute reticulation. 

 Length, 18; width, 12; height, 3 mm. 



Habitat. — San Diego, California, Henry Hemphill. Cat. No. 

 58734 a, U.S.N.M. 



ISCHNOCHITON LISTRUM, new species. 



Chiton of moderate size, straw color, with occasional black blotches 

 on the girdle, which is densely minutely scaled; though the shell is 

 flattish, the dorsum is nearly keeled, but the valves are hardly mucro- 

 nate; the gill row lacks one-fourth of being ambient; the anterior 

 valve has 12, the posterior 11, the intermediate single slits; the anter- 

 ior valve has about 16 thread-like beaded radial riblets, the two 

 marginal ones are large with half a dozen sharp denticles on the 

 edge ; the whole shell is covered under its stronger sculpture with very 

 minute reticulation ; the posterior valve is smaller and has 14 riblets 

 like those on the anterior valve ; the central area is smaller, the mucro 

 being low and behind the center; it is sculptured like the pleural 

 tracts; intermediate valvesAvith a small nearly smooth jugum, the pleu- 

 ral 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. 



Eahitat. — San Diego, California, Henry Hemphill. Cat. No. 

 58734 &, U.S.N.M. 



The peculiar sculpture of the lateral areas is the most conspicuous 

 character of this species. 



