Contributions to Invertebrate Palaeontology. 551 



MOLLUSCA. 

 LAMELLIBRANCHIATA. 



Genus AVICULOPECTERT McCoy. 



Aviculopecteii 1 eqiiilatera. 



Plate XI, fig. 16. 



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

 71, fig. 7.1 



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 border 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 bifurcating 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 

 Marcellus shales, and is readily distinguished from any of those of 

 the Hamilton or other formations by its fine striae and corrugated 

 surface. The stria;, 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, associated with Discina minuta and Leioi^hynchus limitaris. 



Pterinea siniilis. 



Plate XI, fig. 15. 



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



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

 larly 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, distinctly 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 



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

 part I, pi. 1, fig. 18. 



