1S8 PALEONTOLOGY OF NEW-YORK. 



more coarsely pustulose along the deflected line, and nearly or quite 

 smooth towards the margins. 



In the examination of a large number of specimens, the varieties are so 

 extreme that it seems to me difficult to indicate reliable characters for separa- 

 ting this from C. mucronata or C. laticosta; the most distinctive feature being the 

 finer strisB. 



In the specimens referred to C. deflecta there are usually a larger number of 

 strisB, and in some specimens nearly twice as many as the prevailing number 

 in well marked specimens of C. mucronata. The area of the dorsal valve is like- 

 wise much wider in the former than in the latter ; while the interior of the dorsal 

 valve shows stronger muscular imprints, and the surface is not definitely marked 

 by the striae. 



The original of C. gibbosa is a large very convex specimen, with numerous 

 regular even rounded 'striae (fig. 8 b,c, Plate 21), and is more extended on the 

 hinge-line than the usual forms of C. deflecta (fig. 7 a, h, c, Plate 21). 



The illustrations on Plate xxi, figures 1 a-g and 8 a-c, present the usual varieties of 

 form observed in these shells. 



Geological formation and localities. In the Hamilton group, on Canandaigua 

 lake ; and at Ludlowville and Kidder's ferry on Cayuga lake ; at Moscow, York, 

 Covington and other places in Western New- York. 



Cbonetes pusilla. 



PLATE XXL 



Chonelet pvtilla : Hall, Tenth Report on the State Cabinet, p. 149. 1857 

 Compare Chonetea deflecta and C. mucronata. 



Shell small, semielliptical, the length and width being about as two to 



three ; the hinge-line usually about equals the greatest width of the 



shell below. 

 Ventral valve gibbous, regularly convex on the umbo and in the middle 



and lower part of the shell, more abruptly depressed towards the 



hinge-extremities, which are obtuse and rarely a little extended : 



area narrow. 

 DorsAL valve with the concavity nearly corresponding to the convexity 



of the opposite valve : area linear, scarcely exceeding the thickness 



of the shell. 



