238 



valve convex, with ;i moderately high area, divided by an 

 open delthyrium. The teeth arise from the bottom of the 

 valve as two erect divergenl crests. Brachial valve slightly 

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

 chilidium, and a large cardinal process bilobed at, the sum- 

 mit. The brachidium consists of two slender descending 

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

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

 into ;i low median ridge. Surface of both valves plicated. 



Tropidoleptus carinatus. (Conrad.) (Fig. 150.) (Pal. 

 \. V.. Vol. IV., p. 407. PI. LXII.) 



Dist inguishing Characters.— 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; hue undulating concentric surface striae, and occa- 

 sional coarser imbricating lamella?. 



dlvllwi .';!! ll . 1 ,.' / :'"'"" / V / " / ','" s ':"- '""''.''■ J* ntra *} P roflle - and (lf > r sal view of a normal in- 

 dividual, enlargements ol intenorsof pedicle and brachial valves (from Hall). 



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

 four Feet below the Encrinal limestone, at Section G (one 

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



