DISCING OF THE CHEMUNG GROUP. 
25 
Discina alleghania. 
PLATE I. 
Discina alleghania : Hall, 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 stride 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 strise. 
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. 
Discina alleghania. 
Discina newberryi (n. s.). 
PLATE I. 
Shell subcircular or broadly ovate, sometimes oblate : apex situated near 
[ Paleontology IV.] 4 
