ISO 
PALAEONTOLOGY OF NEW-YORK. 
side-of the apex : these are bent a little outward as they leave the 
shell, and then rise almost vertically, or with a slight curve from the 
direction of the hinge-line. 
The surface is marked by from 86 to 40 or 50 slender rounded or sub- 
angular strise on the outer margin. In the upper and middle portions 
of the shell, the striee are increased by bifurcation and intercalation. 
The radial striae are crossed by fine concentric striae. 
This species occurs in the same black. shale with C. mucronata , and may be 
distinguished from it by the more numerous and more frequently bifurcating 
striae, which are*likewise more angular. The direction of the cardinal spines, when 
present, is always a characteristic feature. 
At one time I compared this species with C. scitula; but it is a very marked 
and distinct species, and not readily confounded with any other. In the con¬ 
centric striae it resembles C. logani , but the laminae are closer, less undulating, 
and apparently do not affect the entire structure of the shell as in that species. 
Numerous specimens of casts and impressions of the exterior shell in the Che¬ 
mung group appear to be of this species : these will be illustrated on Plate 22. 
Geological formation and localities. In the thinly lamenated black Marcellus 
shale, at the base of the Hamilton group near Caledonia, N. Y. ; and in the higher 
beds of the same group, as well as in the Genesee slate, on the outlet of Crooked 
lake; but it has not proved an abundant species in any of the localities examined. 
Chonetes scitula. 
PLATE XXL 
Chonetes scitula : Hall in Tenth Report on the State Cabinet, p. 147. 1857. 
Compare Chonetes lineata, etc. this Vol. p. 121. 
Shell transverse, semioval : hinge-line often not quite equalling the 
greatest width of the shell; cardinal angles rarely a little salient. 
Ventral valve moderately gibbous in the middle, and regularly curving 
to the front and basal margins; the gibbous portions narrowing 
towards the hinge-line, and the umbo little elevated; abruptly depres¬ 
sed towards the cardinal angles, which are nearly flat and sometimes 
a little deflected at the extremities. 
Dorsal valve with a concavity less than the convexity of the opposite 
valve; the cardinal angles flat. 
