64 



PALJEONTOLOGT OF NBW-YOHK. 



impossible, therefore, to know precisely what the external characters of the shell are, until we 

 have more perfect specimens. 



Fig. 9 a. The specimen, natural size. 



Fig. 9 J. The crenulated hinge-line, enlarged. 



Position and locality. This shell, with Leptcsna orthididea and L, depressa, occurs in shaly 

 laminated sandstone highly charged with oxide of iron, associated with the iron ore beds in the 

 town of Kirkland, Oneida county. {State Collection.) 



Genus CHONETES (Fischer). 



This genus has the same form as Leplcena, and is distinguished principally by a row of 

 tubular spines on the margin of the dorsal valve bordering the area. 



450. 1. CHONETES CORNUTA. 



Pl. XXI. Fig. 10 a -/. 



Strophomena cornuta. Hall, Geol. Rep. 4th Dist. N. York, 1843. 



Chonetes cornuta. De Koninck, Recherches sur les animaux fossiles, 1847, Part 1, pag. 203, 

 pl. XX, fig. 3 a, b. 



Shell semicircular ; surface covered with fine equal striae, which are equal to the spaces be- 

 tween them ; striae round, straight, bifurcating ; upper margin of the dorsal area with three 

 tubes or spines on each side of the beak ; spines oblique or divergent below, curving inwards 

 at the middle and upper parts, outer ones largest ; area extremely narrow ; interior surface 

 striato-punctate as in Leptjena. 



This shell bears some resemblance to Chonetes lata {Lepta:na lata), Sil. System, pl. 5, fig. 

 13 ; but a comparison of specimens has shown them decidedly distinct species. 



This species is more flat than the small one in the Corniferous limestone and Hamilton 

 group, which it resembles. It is evidently very limited in its geological as well as geographical 

 range. It is commonly seen in the form of casts, the shell being extremely thin and usually 

 separated ; and the spines are often removed with the shell, so that it becomes necessary to 

 rely on the form of the shell, striae, etc., to distinguish the species. 



Fig. 10 a, h. Two specimens of the natural size (ventral and dorsal views), having the spiniform 



tubes attached. 

 Fig. 10 c. A small fragment of green slate, with several valves upon the surface, some of them 



destitute of spines. 

 Fig. 10 d. The dorsal valve enlarged, showing its appearance when magnified to double the 



natural size. 

 Fig. 10 e, /. Enlarged portions of casts of the hinge and dental processes of the dorsal and ventral 



valves, as seen under a magnifier. 



