28 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



botli in the bluish shales and in the dark slaty beds^ which are of the same 

 character as the Genesee slate. 



A single specimen of a ventral ■ valyej found iti the tipper part of the 

 Chemung group in Steuben county, possesses characters so entirely similar 

 to those of the Hamilton group^ that I can find no means of separating it. 



The oval form and excentric position of the apex are sufficient to distin- 

 guish the species from others of these groups. The elliptical specimens 

 measure half an ineh, or usually a little more in length, with a width of 

 nine-twentieths of an inch. 



Geological formation and locality. In the Hamilton group, on the shores 

 of Seneca lake near Ovid, and in the upper part of the group on the shores 

 of the Canandaigua lake ; and in the green shale of the Chemung group Id 

 the south part of Steuben county, at Troupsburgh. 



^^DISCINA (sp.?).'^ 



A small nearly circular specimen of a ventral valve, occurring in 

 the Marcellus slate, is marked by fine crowded and scarcely 

 distinct striss : the apex is excentric, being scarcely more than 

 one-third the length of the shell from the posterior margin ; 

 with a short, narrowly oval foramen. 



This specimen is unlike any other one before me, and may be a distinct 

 species ; but I hesitate to designate it without more material. 



Geological formation and locality. In the Marcellus slate ; near Bridg- 

 water, Oneida county. 



^' BISCINA TULLIA ( n. s.)." 



Dorsal valve elliptical ; apex excentric, elevated above the plane 

 of the margins of the shell nearly one inch ; length half an inch, 

 and breadth little more than three-tenths of an inch. 



Surface marked by fine crowded stride. 



A single specimen of the dorsal valve only has been seen, but its pro- 

 portions of length and height distinguish it from any other species in the 

 rocks of New-York. 



Geological formation and locality. In the Tully limestone near Ovid, 

 Seneca county. 



" DISCINA TEUNCATA ( n. s.)." 



Shell ovate, the anterior end broader : valves depressed-convex. 

 Dorsal valve with the apex near the posterior margin, and 

 directed backwards ; posterior margin very abruptly rounded 

 or truncate. Ventral valve with the apex submarginal ; foramen 

 extending nearly or quite to the posterior margin, which is 

 indented. 



