CHAZY LIMESTONE. 21 



32. 1. ATRYPA DUBIA (n. sp.). 



Pl. IV. (bis). Fig. 5. 



Obovate ; beak of the dorsal valve extended, rounded and incurved ; front scarcely 

 depressed ; surface marked by 30 or more radii. 



The specimen described has nearly all the shell removed, and presents only the characters 

 of a c£ist. The impressions of the radii are distinctly marked in the cast. I have observed 

 but two or three individuals of this species. 



Position and locality. In the higher semi-oolitic layers of the Chazy limestone, Chazy, 

 Clinton county. (State Collection.) 



33. 2. ATRYPA ACUTIROSTRA ( n. sp.). 



Pl. IV. (bis.. Fig. 6. 



Obovate, minute ; base rounded ; beak acute, acuminate ; surface marked with prominent 

 equal radii ; dorsal valve convex, elevated along the middle ; ventral valve convex, with 

 a depressed line along the centre ; surface marked by about 12 or l4 equal rounded di- 

 verging radii, the central one on the dorsal valve often extending only half way to the 

 beak. 



This fossil is usually very minute, and, on that account, frequently overlooked ; but 

 when once observed,. its characters are sufficiently decisive. The beak is incurved, ending 

 in a sharp point, which is often broken in detaching the specimen from the rock ; the radii 

 are strongly marked, and the obovate form is usually well preserved. 



Fig. 6. The two lower figures are of the natural size ; the upper one is enlarged. 



Position and locality. In the higher layers of the Chazy limestone, in considerable num- 

 bers ; also in the oolitic portions of the metss, Chazy village, and near Galway, Saratoga 

 county. (State Collection.) 



34. 3. ATRYPA PLENA (n.jp.). 



Pi.. IV. (big). Figs. 7 a, b, c, d, e. 



Compare Terebratula tripartita of the Silurian System, pi. 21, fig. 15. 



Somewhat quadrangularly gibbous or rotund ; front margin elevated in a moderately 

 deep sinus ; beak of the dorsal valve small, closely incurved over the beak of the ventral 

 valve ; surface marked by 16 to 20 strong radii, about four or five of which are depressed, 

 forming the sinus of the dorsal valve, and an equal number elevated above the others on 

 the ventral valve. 



