!•« PALiEONTOLOGY OF NEW-YORK. 



Fig. 1 d. A specimen showing the corrugations more strongly. 



Fig. 1 e. An individual of full size in wliioh tbe corrugations are well developed. 



Fig. 1 f, g. Dorsal and ventral sides of an entire individual. 



Fig. 1 k. Profile view of the preceding specimen. 



Fig. 1 I. An old specimen where the corrugations are much stronger and closer than usual. 



Fig. 1 k, I, m. The interiors of several ventral valves, showing the area, crenulated hinge 

 line, muscular and vascular impressions, etc. 



Fig. 1 n. Area of the ventral valve. 



Fig. 1 r. A portion of the area enlarged, showing the striated surface and crenulated margin. 



Fig. 1 s, f. Portions of the casts of the ventral valve of two different individuals, showing 



some slight difference in the character and strength of the impressions. 



Geological position and locality. In the shaly limestone of the Lower Heldcrberg 

 group : Helderberg mountains; Schoharie, Cailisle, Catskill, Hudson, etc. 



The following species have no crenulations on the hinge line, and have 

 broad triangular foramina, more or less closed by a pseudodeltidium, 

 leaving the form of the foramen distinctly visible. 



Stroplioniena woolwortliana ( n. s.). 



Plate XVII. Fig. 1 & 2. 



Shell semielliptical, often extremely elongate. Ventral valve concave 

 towards the front and flat on the lateral margins, depressed convex 

 near the beak : beak small, and scarcely rising above the edge of the 

 valve. Dorsal valve convex, most elevated near the front, and flattened 

 towards the umbo : beak not projecting. Hinge line straight, equal to 

 the greatest width of the shell. Area linear, conspicuous, partly common 

 to both valves. Foramen broadly triangular, partially or entirely closed. 



Surface finely striated. Striae round, crowded, simple, increasing by 

 interstitial addition, concentrically crossed by closely arranged striae 

 and a few distant lines of growth. 



Ventral valve marked interiorly by a broad flabellate vascular area, 

 which is partially limited by the dental lamellae : teeth strong, pro- 

 jecting more or less into the interior of the valve ; in old shells, less 

 conspicuous. Dorsal valve with vascular area strongly marked : cardi- 

 nal process deeply bifid, and each division again trilobate upon the 

 exterior side ; lateral lamellae curving as in Orthis. 



