ISCHNOCHITON. 73 



V30, f. 2, 2a, 2b. DALL, Bull. U. S. Nat. Mus. 37, p. 172, t. 45, 

 f. 2. 



This species is readily distinguished from T. albus by the 

 very distinct differentiation of the valves into median and lateral 

 areas, having lines of sculpture running in different directions, and 

 by the much coarser granulation of their surfaces. In T. albus 

 there are no distinct lateral areas ; the radiating grooves and ridges 

 are absent; and the granulation is so fine and obscure as to be 

 scarcely visible without a lens. The spinulation of the marginal 

 membrane is similar in the two species. ( Verrill.) 



I. DENTIENS Gould. PI. 8, figs. 61-65. 



Shell oval, rather elevated, dorsally angled, ash colored, closely 

 and finely mottled with olive, and having a series of alternating 

 olive and light spots upon the back edges of the valves along the 

 sutures. These spots are often obscure or wanting, and in some 

 specimens the ground color is a pale orange-flesh tint. 



The valves are covered with a very minute sharp granulation, 

 the granules small but well raised, and on the central areas of some 

 specimens they are somewhat disposed to be arranged in longitud- 

 inal lines converging toward the dorsal ridge, this disposition usu- 

 ally stronger toward the lateral extremities of the valves. The 

 lateral areas are a little raised, the diagonal lines separating them 

 from the central areas rather distinct. The umbo of the posterior 

 valve is median, somewhat raised, the slope behind it being 

 depressed and concave. 



The interior is either whitish stained with gray-green, or quite 

 green. The sutural plates do not project as far as usual, and on 

 some valves they are emarginate in front. The jugal sinus is wide, 

 angular, flat or encroached upon by the jugum. The anterior 

 valve has 11 slits in the insertion plate, the intermediate valves 1, 

 the posterior valve has 10 or 12, and some of the median teeth are 

 bifid at the tip. 



The girdle is narrow, gravelly, covered with minute scales. 



The gills extend to the front end of the foot. 



Length 15, breadth 10 mill. 



Paget Sound (Gld.) ; San Diego, California (Hemphill, in A. N. 

 S. P. coll.). 



Chiton dentiens GOULD, Proc. Bost. Soc. N. H. ii, p. 145; Otia 

 p. 6. C/i. (Onithochiton') dentiens GLD., 1. c., 242; U. S. Expl. 



