PRODUCTELLiE OF THE CHEMUNG GROUP. 
177 
Geological formation and localities. The original specimens are from the Che¬ 
mung group, on Twenty-mile creek in Chautauque county. It occurs at Leon and 
New-Albion in Cattaraugus county; and west of Olean in Allegany county, New- 
York. 
Productella striatula (n. s.) 
PLATE XXV. 
Body of the shell subovate; outline semielliptical, the length equalling or 
greater than the width : hinge-line equalling, or sometimes a little 
greater than the width of the shell. 
Ventral valve deeply convex, ventricose in the middle and on the 
umbo, abruptly depressed at the sides and the cardino-lateral angles, 
'forming small ears; regularly arching towards the front, which is 
more or less produced : umbo elevated above the hinge-line, and the 
apex closely incurved. 
Dorsal valve somewhat deeply concave; the upper part, to near the 
middle of its length, often slightly concave, and abruptly deflected 
towards the front : the deflected portion is sometimes more than half 
the length. 
Surface of ventral valve, where the shell is entire, finely striate con¬ 
centrically, strongly wrinkled on the ears, and the folds usually be¬ 
coming obsolete on the middle of the shell, but sometimes they are 
retained in considerable strength. Numerous slender spines are dispo- 
• sed in somewhat regular concentric ranges along the front and middle 
of the shell, while they are often irregularly disposed and sometimes 
absent from the umbo and upper middle portions of the shell, but are 
always present on the ears. When the shell is partially exfoliated, the 
surface is marked by fine closely arranged radiating striae. Where the 
shell is entire, the spines rise almost vertically from* the surface, with 
scarcely elongate ridges at their base, while in the exfoliated surface 
they leave oval depressions around the spine-bases; but this character 
is subject to variation from-the nature of the matrix. 
The interior surface of the dorsal valve only is known; this is finely 
[ Paleontology IV.] 23 
