286 NORTH AMERICAN INDEX FOSSILS. 



250. C. lamellata Hall. (Fig. 349.) Siluric, 

 Small, subrhomboidal. Surface with six to seven simple plica- 

 tions on each side of fold and sinus ; usually but two plications in 



<v sinus and three on fold. Entire shell crossed 



0h m by strong, imbricating, concentric lamellae 



which are conspicuously arched over the pli- 

 cations, giving the surface a rugose appear- 

 ance. 

 Fig. 349. Camarotoe- Upper Siluric (Cobleskill, etc.) of New 

 xhia lamellata (Pal. N. York, New Jersey, Pennsylvania, Maryland 

 ''' and West Virginia. 



251. C. litchfieldensis Schuchert. (Fig. 350.) Siluric. 

 Large, robust. Length and breadth subequal. Umbo of ped- 

 icle valve large and prominent. Surface with 16 to 18 plications, 



of which three and four occupy respectively the rather narrow and 

 unpronounced sinus and fold. 



Cobleskill and Rondout of New York. 



252. C. semiplicata (Conrad). (Fig. 351.) Devonic. 



Subtriangular. Valves nearly equal. Surface smooth in upper 

 portion with low plications toward the front, one to two of which 

 occupy the shallow sinus and two to three 

 the low fold ; a few (one to four) are present 

 on each side of fold and sinus. Very similar 

 to C. acinus, but the angle at the beak be- 

 tween the cardinal slopes is larger, the sinus 

 and fold are more pronounced and the 

 shell is larger, averaging about « inch in FlG - 35i- Gw 



, A . , .. ~> h 11 chia semiplicata (Pal. N. 



length, while C. acinus averages only about Y . ill 

 A inch. 



Helderbergian (Coeymans) of New York. 



o % 



