I6« PALEONTOLOGY OF NEW-YORK. 



Disoina vannxomi ( n. s.)- 



Plate VIII. Fio. 1 a, b. 



Shell orbicular or broadly subelliptical. Dorsal valve very convex : apex 

 excentric, and pointed towards the posterior extremity of the shell. 



Surface marked by fine closely arranged concentric stria? and finer 

 radiating stria3, exhibiting a finely cancellated appearance under a 

 magnifier. Inferior valve unknown. 



This species differs but little in form from D. disctts. The dorsal valve is much 

 more convex, the beak somewhat acute, and the concentric striae more closely 

 arranged. 



A single individual only of the dorsal valve has been found, and I am unable 

 therefore to speak of the variety it may exhibit when studied with more specimens. 



Fig. 1. Profile view. 



Fig. 1 a. Dorsal view, showing the form of the shell. 



Fig. 1 b. Enlargement of surface, showing the radiating and concentric striae ( the latter 

 are not strong enough in proportion to the others). 



Geological position and locality. In the upper part of the Waterlime group : 

 Quarry northwest of Manlius-square. 



% 



Oithis oblata ( n. s.). 



Plate X. Fia. 1 - 22. 



Compare Orthis hybrida, Mi'RcnisoN, Sil. System, p. 63, pi. 13, f . 11 ; also Pal. N.Y. Vol. ii. 

 " Orihis orbicularis, SowERBr. 



" Orihis vanuxemi of the Hamilton group, N.Y. 



Shell in the young state longitudinally subovate, and varying from 

 circular to transversely oval in its stages of growth, resupinate. Ven- 

 tral valve convex at the beak, flattened in the middle, and concave 

 towards the front. Dorsal valve very convex in the middle and towards 

 the beak : beaks of the two valves nearly equally elevated ; that of 

 the ventral valve pointed : area very small : foramen large. 



Surface finely striated : striae frequently bifurcating and curving towards 

 the lateral and cardinal margins, concentrically marked by finer striae 



