288 NORTH AMERICAN INDEX FOSSILS. 



2$6. C. sappho Hall. (Fig. 354, c,d.) Devonic-Mississippic. 



Large and robust, broader than long. Pedicle valve depressed- 

 convex with abruptly acute apex. Brachial valve gibbous, regu- 

 larly arching transversely. Surface marked with 20-24 strong, 

 angular plications. 



Marcellus-Waverly of New York, Ohio. 



257. C. contracta Hall. (Fig. 352, d-g.) Devonic-Mississippic. 

 Subquadrate, abruptly and deeply sinuate. Pedicle valve very 



slightly convex, often becoming almost flat near the front and 

 marked by a broad angular sinus. Brachial valve somewhat 

 gibbous in the middle and regularly convex transversely, marked 

 by a mesial fold. Surface with 16-20 angular plications of which 

 there are 4 on fold and 3 in sinus. 



Portage-Waverly of New York, Pennsylvania, Ohio. 



258. C. sageriana (A. Winchell). Mississippi. 

 Of medium size. Brachial valve quite convex with a prominent 



and inflected beak and about 16 obtuse radial plications, some of 

 the central ones showing a groove on the summit toward the front. 

 Mesial fold developed only at front of valve where it consists of 2 

 or 3 slightly elevated plications. 



Marshall of Michigan, Waverly of Tennessee, Ohio. 



LXXVII. Stenochisma. 



Differs from Camarotcechia 

 in wanting the median septum 

 of the brachial valve with its 

 subcardinal cavity; and in 

 having the hinge plate divided 

 by a median fissure which ex- 

 tends to the bottom of the 

 shell and contains a slender 

 cardinal process. Devonic. 



259. S, formosum (Hall). 

 (Fie;. 3Sv) Devonic. 



Fig. 355. Stenochisma formosum (Pal. N . v & ° J J ' 



Y ln \ Subtriangular, the lateral 



margins forming an angle at 

 the beak of 90 to 1 10°. Beak of pedicle valve prominent and 

 arched. Brachial valve the more convex. Surface marked with 

 20 to 24 simple, angular plications on each valve, 2 to 4 of which 

 occupy sinus and fold. 



