270 CALLTSTOCHITON. 



Callistochiton decorat us CPR., MSS. Chiton ( Callistochiton) decor- 

 atus Cpr., ORCUTT, Proc. U. S. Nat. Mus. viii, p. 544 (1885,) no 

 description. 



It has been reported from San Diego by Orcutt and from La Paz 

 by Carpenter (Pease coll.) 



The partially sculptured central areas are peculiar and character- 

 istic, and the tail valve presents features not found in the other 

 species of the same region. The figures 17-20 may be regarded as 

 the types, but some individuals show some very obsolete coarse ribs 

 in the front part of the jugal smooth tract. 



The type is in the collection of the Academy. 



C. GABBI Pilsbry, n. sp. PL 60, figs. 7-10. 



Shell oblong, convex, rather sharply carinated, the side-slopes 

 somewhat convex. Surface lusterless, the central areas light brown, 

 lateral areas olivaceous-brown. 



Median valves not beaked ; lateral areas composed of two strongly 

 elevated ribs, bearing acute grains, the posterior rib wider, having 

 an additional row of smaller grains along the sutural margin ; the 

 sulcus between the ribs rather wide, minutely pitted. Central areas 

 having about 15 parallel longitudinal riblets, becoming diverging 

 toward the outer margins, the interstices very closely, sharply cross- 

 latticed ; region of the beaks smoother, pitted and microscopically 

 granulate. Anterior valve having 9 strongly elevated ribs separated 

 by pitted intervals of the same width as the ribs, the latter bearing 

 acute grains; the posterior rib on each side wider, with sutural 

 grains ; region of the beak excavated. Posterior valve elevated at the 

 front edge, rapidly sloping backward, the mucro about central, much 

 depressed ; posterior area sculptured with 7 rather broad wave-like 

 radiating ribs surmounted by acute grains. 



Interior light olivaceous, with dark markings under the beaks. 

 Sutural plates well developed, separated by a narrow, angular, con- 

 vex sinus. Anterior valve having 9, central 1, posterior valve 8 

 slits ; teeth rather short, smooth, festooned and slit at the ribs. Eaves, 

 especially in the tail valve, extremely narrow. 



Girdle covered with very compactly imbricated, wide, finely 

 striated scales, which are arranged in alternate patches of olive-bluish 

 and lighter, the light patches being composed of mingled bluish, 

 tawny and white scales (fig. 7.) 



Length 14, breadth 8 mill. ; divergence about 110. 



Gulf of California (Gabb.) 



