PRODUCTELL^ 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. 



Venteal 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 th§;.^pine-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 

 [ Paljsontology IV.] 28 



