128 
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 strige. 
In the specimens referred to C. deflecta there are usually a larger number of 
strias, 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 strise. 
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 , 6, c, Plate 21). 
The illustrations on Plate xxi, figures 7 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. 
Chonetes pnsilla. 
PLATE XXI. 
Chonetes pusilla : Hall, Tenth Report on the State Cabinet, p. 149. 1857 
Compare Chonetes 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. 
