DISCING OP THE CHEMUNG GTROUP. 



^ 



Discina alle^hania. 



PLATE I. 



DUcina alleghania : Hali, Thirteenth Report on the State Cabinet, p. 77. 



Shell broadly elliptical or nearly circular. Dorsal valve depressed conical; 



anterior side broadly and equally convex ; apex placed at a little more 



than one-third the length from the posterior end of the shell, slightly 



inclined backwards ; the posterior slope concave, and the shell flattened 



towards the margin. 

 Surface marked by fine regular concentric lamellae, which are distant 



from each other two or three times their width. 



This large species is one of the finest and most beautiful of the genus, nearly 

 equal in size to the D. ampla of the Oriskany sandstone, and differing from that 

 one in the posterior position of the apex and the more abrupt sloping on the 

 posterior side, while the concentric striiB are much finer and more closely ar- 

 ranged. It differs from the large circular form D. discus of the Lower Helderberg 

 group, in the greater elevation of the dorsal valve, and absence of radiating stride. 



This species differs from the D. grandis of the Hamilton group in the position 

 of the apex of the dorsal valve, and in the direction of the foramen relative to 

 the greatest diameter of the shell. 



Geological formation and locality. In the Chemung group, Hobbieville, Allegany 

 county, N.Y. 



Discing allxshaxia. 



Dlscina newberryi ( n. s.). 



PLATE L 



Shell subcircular or broadly ovate, sometimes oblate : apex situated near 

 [ Pai.jjoxtologv IV.] 4 



