238 



valve convex, with a moderately hiji'h area, divided l»y an 

 Oj)en delthyrinni. The teeth arise from the liottom of the 

 valve as two erect divergent crests. Brachial valve sliiihtly 

 concave, or nearly flat, with a low area, a prominent convex 

 chilidinm, and a large cardinal process bilobed at the snm- 

 mit. The brachidium consists of two slender descending 

 lamelhe, which unite near the middle of the valve with a 

 sharp, thin median septum, which, towards the beak, passes 

 into a low median ridge. Surface of both valves plicated. 



Troimuoleptus cAKiXATi'S. (Courad.) (Fig. 150.) (Pal. 

 N. Y., Vol. IV., p. 407. PL LXII.) 



Distinguishing Chnracters. — Strophomenoid outline; 

 broad, simple, rounded plications, wider than the inter- 

 spaces; broadly sub-carinate center of pedicle valve, caused 

 by the greater width and prominence of the central plica- 

 tion ; longitudinally striated, convex chilidium of brachial 

 valve; fine undulating concentric surface strifv, and occa- 

 sional coarser imbricatin<i- lamelhe. 



'^-^^ 



t^a t»ltl* m t w wi- ' ■MU ^y I fc 



Fio. 150. Tropidoleptus carinatus. Ventral, \iu liU .m 1 iK ] ^ il views of a normal in- 

 dividual; enlargements of interiors of pedicle and biaclnal \al\e-, i^tiumHall). 



Found in the Encrinal limestone, at Section 5 (common); 

 four feet below the Encrinal limestone, at Section 6 (one 

 specimen) ; seventeen to twenty-one feet below the Encrinal 



