CHITON. 159 



This species is amply distinguished from C. Icevigatus by the wider 

 sinus, different coloring, and by the much more porous lines radiat- 

 ing toward the slits, and the conspicuously porous triangle under the 

 dorsal ridge of each valve, as shown in fig. 75. 



Species of the West coast of the Americas. 



This is a natural group of large species, characterized by the 

 generally somber color, large smooth scales, and anterior mucro. 

 Radsia is a tangent from this circle of species. 



C. L2EVIGATUB Sowerby. PI. 34, figs. 68, 69, 70, 71. 



Shell oval, subdepressed or elevated, carinated, the side-slopes 

 somewhat convex. Surface smooth. Colors soft and blended, vary- 

 ing from purple-gray to olive, lighter in the middle, where there are 

 three irregular longitudinal series of black or dark blotches ; back 

 edge of each valve often articulated with light and dark spots. 



The lateral areas are a little raised ; whole surface polished, show- 

 ing a microscopic quincuncial granulation under the lens. Mucro 

 unusually close to the front edge of the tail valve, almost marginal. 



Interior dark green-blue ; the sutural plates lighter but having a 

 large dark green or blackish blotch at the base of each. Sinus deep, 

 square, with a convex row of jagged teeth. Anterior valve having 17, 

 central valves 1, posterior valve 21 narrow slits; teeth blunt, deeply 

 laciniate ; eaves short, narrow, spongy. 



Girdle wide, tessellated with alternate light and dark. 



Length 55, breadth 38 mill. 



Length 85, breadth 55 mill. 



Gulf of California to Acapulco. 



Chiton Icevigatus SOWB., P. Z. S. 1832, p. 59 ; Conch. Illustr., f. 

 18*. REEVE, Conch. Icon., t. 7, f. 35. Chiton articulatus SOWERBY ; 

 P. Z. S. 1832, p. 59; Conch. Illustr., f. 18. REEVE, Conch. Icon.,' 

 t. 2, f. 7. 



Sowerby's description of Icevigatus precedes that of articulatus in 

 the P. Z. S., and since the two forms prove to belong to one 

 species, the former name must be accepted. Fig. 69 represents the 

 articulatus. 



There is considerable variation in the degree of elevation and in 

 the contour, but the extremes seem to be connected most intimately 

 by- specimens intermediate in form. This species has a general 



