184 
PALAEONTOLOGY OF NEW-YORK. 
This species is quite distinct from any of those already described. In its mesial 
sinus, it resembles the P. boydii; but it is usually a much more convex shell, and 
in all the specimens has fewer spines on the ears, and none upon the middle of 
the shell. The spines and spiniferous tubercles are likewise of a different charac¬ 
ter, while the form and expression of the shell is very different. Occurring only as 
casts in sandstone, the entire characters cannot be ascertained. 
Geological formation and locality. In sandstone of the age of the Chemung 
group, at Meadville, Pennsylvania, associated with Spirifer disjunctus and other 
fossils of the age of the Chemung group. 
Productella oniista (n. s.). 
PLATE XXVI. 
Shell large, broadly semielliptical in outline, the length and breadth 
about as four to five : hinge-line about equalling the width of the 
shell, the convexity nearly hemispheric. 
Ventral valve regularly convex, depressed-convex in the smaller indi¬ 
viduals and ventricose in the older ones, regularly rounded and curv¬ 
ing to the front and baso-lateral margins. Body of the shell abruptly 
curving towards the umbo, which is elevated above the hinge-line, 
and the apex closely incurved; abruptly depressed, and concave be¬ 
tween the umbo and the cardinal extremities, which are produced in 
ears comparatively wide, nearly flat, and usually a little rounded at 
the extremities. 
Dorsal valve broadly and deeply concave, corresponding to the ventral 
valve, with the hinge-line comparatively a little shorter. 
Surface of the ventral valve with obscure radiating and concentric strise 
and a few wrinkles on the ears, which are partially extended to the 
body of the shell. These wrinkles of the cardinal margins are studded 
with the bases of slender spinesf and the entire surface is marked by 
concentric rows of similar but smaller spiniferous tubercles. On the 
shell, these rise almost directly from the surface without any elonga¬ 
tion ; but where the shell is exfoliated, the remaining pustules are 
elongate. 
The partially exfoliated ventral valve is peculiarly punctate or pitted, 
as if by the most minute corrugation. The entire cast is puncto-striate, 
presenting an unusual marking. 
