552 Contributions to Invertebrate Palseontology. 



constricts the margin of the shell ; posterior wing one-third longer than the 

 anterior side, pointed at the extremity and sinuate below. Body of the valve 

 ventricose, strongly so on the umbone, with a strong, tumid beak, which pro- 

 jects distinctly beyond the hinge. Surface of the left valve marked by dis- 

 tinct radii, whicli plainly alternate in strength over the body of the valve, 

 but less distinctly so toward, and on the wings ; also, by less strong concentric 

 lines, and varices of growth. Right valve unknown. 



The shell is of the tj^pe of Pterinea decussata Hall, which occurs 

 abundantly in the Hamilton group in New York, but is of extremely 

 small size, and very ventricose ; the proportionally strong varices 

 of growth showing its adult character. The type is one repre- 

 sented in the Devonian rocks, from the Hamilton to the top of the 

 Chemung, inclusive, in New York, b}^ several distinct species, but 

 which is seldom recognized below this horizon. We may, there- 

 fore, consider it as an additional evidence of the age of the beds in 

 which it is found. 



Formation and Locality. — In the thin shaly layers of bitumi- 

 nous limestone, from above the " Bone-bed" at Smith and Price's 

 quarries, near Columbus, Ohio. 



