284 



NORTH AMERICAN INDEX FOSSILS. 



i / . Shell not ventricose a '. 



a' ' . Pedicle valve with small, closely incurved beak. 



245. C. plena, 

 a'. Pedicle valve with large, not closely incurved beak. 



251. C. litchfieldensis. 



c. Plications few (9-14) 2'. 



2 r . Angle at beak between cardinal slopes less than 90 . 



248. C. indianensis. 



2' '. Angle at beak greater than 90 249. C. ivhitei. 



3. Pedicle valve flattened d. 



d. Sinus and fold with 2-4 plications 257. C. contracta. 



d. Sinus and fold with 5 or 6 plications 253. C. tethys. 



245. C. plena Hall. 



(Fig. 345-) 



Fig. 345. Camar otcechla plena (Canadian 

 Geol. Surv. ). 



Ordovicic. 

 Gibbous. Pedicle valve 

 with small beak closely in- 

 curved over that of the bra- 

 chial valve. Surface of each 

 valve marked with 16-20 

 strong radial plications, 

 about 4 or 5 of which oc- 

 cupy the sinus and fold. 

 Chazy of New York, Ontario, Quebec. 



246. C. neglecta Hall. (Fig. 346.) Siluric. 

 Small. Brachial valve the more convex. Sides sloping ab- 

 ruptly from beak. Plications 8— 1 3. Strongly defined sinus and 

 fold, the former with 3, the latter with 

 4 plications. Deep frontal emargination 

 present. 



Clinton and Niagaran of New York, 

 Ohio, Indiana, Wisconsin, Ontario, 

 Nova Scotia. 



247. C. acinus Hall. (Figs. 347, 348, 

 upper row.) Siluric. 

 Small, longitudinally ovate, narrowed 



toward the beak and truncate in front. 

 Valves of nearly equal convexity. Surface marked by few plica- 

 tions of which there is one in the very low sinus of the pedicle 

 valve and two in the inconspicuous fold of the brachial. 

 Clinton of New York, Niagara of Indiana, Kentucky. 



248. C. indianensis (Hall). (Fig. 348, middle row.) Siluric. 

 Subtriangular, moderately biconvex. Length and width nearly 



w $fo 



4b 



Fig. 346. Camarotaechia neg- 

 lecta (Pal. N. Y. II.). 



