PALEONTOLOGY. 445 



MOLLUSCA. 



LAMELLIBRANCHIATA. 



Genus AVICULOPECTEN McCoy. 



Aviculopecten f equilatera. 



Plate VII, fig. 16. 



Avicula equilatera Hall, Rept. 4th Dist. Geol. Surv. N. Y., 1843, p. 180, Table 71, 

 fig. 1\ 



Shell small and slightly oblique, somewhat trapezoidal in outline, hinge-line 

 straight and as long as the greatest length of the shell ; beaks nearly central on the 

 hinge ; anterior cardinal angle mucronate, and the anterior border gradually sloping 

 backward from the point ; basal broader broadly rounded ; posterior margin slightly 

 extended at the lower third beyond the extremity of the hinge, and also slightly 

 sinuate above to form the sulcus of the posterior wing, which is small and rounded. 

 Surface of the valves very depressed convex, and marked by numerous fine bi fur- 

 cating radii, and also by several concentric undulations which give to the shell a 

 strongly corrugated appearance. 



The species is, in New York, a very characteristic form of the Mar- 

 cellus shales, and is readily distinguished from any of those of the Ham- 

 ilton or other formations by its fine striae and corrugated surface. The 

 strise, although somewhat increasing in strength toward the margin, are 

 frequently bifurcated so that the increase in strength is not equal to that 

 of simple radii. 



Formation and Locality.— -In the bituminous shale from above the 

 "Bone-bed" at Smith and Price's quarries, near Columbus, Ohio, asso- 

 ciated with Discina minuta and Leiorhynchus limitaris. 



Pterinea similis. 



Plate VII, fig 15. 



Pterinea similes Whitf., Ann. N. Y. Acad. Sci., 1882, p. 214. 



Shell small, oblique; the body, exclusive of the wings, being almost regularly 

 although obliquely ovate in outline, the anterior part being the larger ; hinge-line 

 about two-thirds as long as the entire length of the valve ; anterior wing small, dis- 

 tinctly rounded on the end, and separated from the body of the shell, on the left 

 valve, by a distinct sulcus along the surface, and which constricts the margin of the 

 shell; posterior wing one-third longer than the anterior side, pointed at the ex- 

 tremity and sinuate below. Body of the valve ventricose, strongly so on the um- 

 bone, with a strong, tumid beak, which projects distinctly beyond the hinge. Sur- 

 face of the left valve marked by distinct radii, which 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 type of Pterinea decussata Hall, which occurs abund- 

 antly in the Hamilton group in New York, but is of extremely small 

 size, and very ventricose; the proportionally strong varices of growth 



l This is probably the A. {Pterinopecten) invalidus Hall, of Pal. N. Y., vol. 5, 

 part I, pi. 1, fig. 18. 



