130 PALEONTOLOGY 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 36 to 40 or 50 slender rounded or sub- 

 angular striaB on the outer margin. In the upper and middle portions 

 of the shell, the striae 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 bo 

 distinguished from it by the more numerous and more frequently bifurcating 

 strias, 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 Marcellua 

 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 



ChoneUt icitula : 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. 



Venteal 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. 



