^4 Cinci)i)Hiti, Society of NafAiral IJ istory. 



NUCULITES YOLDIAFOKMIS, U. Sp. (Phlte VII., fig. 20). 



Sliell small, extremely elongate, about three times as long as high: 

 hinge line straight; beaks small, not prominent, somewhat pointed, 

 and situated about three-eighths of the length of the shell from the 

 anterior extremity; posterior end acutely pointed ; margin of anterior 

 end, below its junction with the cardinal line, regularly rounded; basal 

 line genth' curved, slightly sinuate or straightened posterior to the 

 middle of the shell; an undefined and very shallow sulcus crosses the 

 shell obliquely from below the beaks toward the posterior basal mar- 

 gin, causing the straightening of the basal line; cardinal slope nar- 

 row, carrying tw^o folds or ridges, which originate just behind the 

 beaks, extending to the posterior extremity, and gTaduall^' becoming 

 heavier until that point is reached. 



A strong clavicle extends from the anterior cardinal line, just in 

 front of the beaks, nearly to the anterior basal margin. 



Surface marked with ver^' fine concentric lines. 



It is quite impossible to confound this species with any other lamel- 

 libranchiate shell found in the Hudson River Group. 



Formation and localit\': in the shales of the lower part of the Hud- 

 son River Group, at Covington, Ky. 



Collectors: H. E. Dickhaut, E. O. Ulrich. 



Pterinea muckonata, n. sp. (Plate VII., fig. 21), 



(Ety.— From mucro, a sharp point). 



Shell small, broadly semi-cordate in outline,with hinge-line much long- 

 er than the body of the shell; greatest length generally nearly twice the 

 breadth; anterior side gently and regularl}^ convex, forming an angle 

 of about seventy-five degrees with the hinge line; posterior side very 

 slightly concave, or straight below the angle, and gently convex in the 

 lower half, forming an angle of forty degrees with the hinge line; pos- 

 terior wing compressed, extended into a rather long, acute point, and 

 in most specimens is scarcely distinguishable from the rest of the pos- 

 terior portion of the shell; there is no wing at the junction of the 

 hinge with the anterior margin, the shell at that point usually being 

 rounded or obtusely angulated; basal margin regularly rounded. Left 

 valve moderately convex below and at the umbones; beak small, very 

 slightly or not at all elevated above the hinge, and situated between 

 one fourth and one fifth of the length of the hinge line from the ante- 

 rior angle. Right valve not observ^ed. In very young specimens the 

 hinge line is cfmiparatively shorter than in the adult examples. 



