rpenter ha- i:ivn a varietal mum- to a broad, worn specimen, 

 which he thus describes : 



Var. solidus (pi. 15, fig. 97). Very solid, wide, ashen; inside 

 whitish, the posterior valve with 10, central valve 2-3, anterior 

 valve 12 slits. Length 72, breadth 40, divergence 130. 



Carj at* ///, near Sta. Barbara, California. 



This is scarcely more than an individual variation. The figure 

 ivpn-mts the valves only of the type specimen. The mantle is 

 normal. The sculpture is worn away except at the edge. It has 

 evidently lived in a very exposed situation. 



Suhgenus III. ISCHNOPLAX Carpenter. 



LchnnjJ,i.r('i-ii. (Table of Reg. Chit. 1873), DALL, Proc. U. S. 

 Mus. 1878, p. 330, type C. pectinatus Sowb. 



Body elongated, elevated, the valves having high suttirM plates 

 ami strongly elevated lateral areas; mucro posterior, elevated; 

 girdle clothed with very minute imbricating scales and having larger 

 conspicuous striated scales scattered among them. 



The girdle is like that of Heterozona, but the valves and general 

 shape are similar to Stenoplax, except that the mucro is posterior 

 and elevated, a character recalling Callistockiton. 



I. i IX-TINATUS Sowerby. PL 17, figs. 25-30. 



Shell elongated, narrow, elevated ; gray, mottled and dotted all 

 over with black, more or less stained in places with pink. 



The valves are strongly convex ; end valves radiately coarsely 

 granose-ribbed ; umbo of posterior valve elevated, situated behiu<! 

 the center. Lateral area much raised, having radiating granose 

 riblets ; central areas having smaller cords, which are close and lon- 

 gitudinal on the jugum, but become more spaced, coarser, and 

 [liny on the pleura or sides of the central areas. 



Interior bright pink. Anterior valve with in- 12, intermediate 

 valve 1, posterior valve 8-11 slits. Teeth sharp, frequently bifid ; 

 eaves unusually wide, solid, scalloped by the sculpture of the out- 

 side. Sut u nil plates high, rounded. Sinus deep, square. 



Girdle (pi. 1 7, figs. 28, 29) covered with extremely fine scales among 

 which larger, long fiat scales are irregularly scattered. 



Length 36, breadth 16 mill. 



Length 40, breadth 17 mill. 



Cuba (Cuming) ; Guadeloupe (Swift) ; Barbados (Rush). 



