ir4 PALEONTOLOGY OF NEW- YORK. 



Ortliis pedancularls (n. s.)- 



Plate XIII. Fio. 16 a - c. 



Shell subplanoconvex ? Ventral valve with the area about one-third as 

 high as wide, the width equal to half the width of the shell : beak 

 slightly incurved : teeth strong : muscular impressions very deep and 

 strong. 



Surface finely striated. 



I have but a fragment of this species, which, in its general aspect, bears much 

 analogy to O. perelegans and 0. subcarinata ; but the area is proportionally much 

 higher, and the beak less incurved than in either of those, while the muscular 

 imprints are much larger and stronger. Other specimens are required for a complete 

 comparison and description. 



Fig. 16 a. Exterior of an imperfect ventral valve. 

 Fig. 16 6. Interior of the same. 

 Fig. 16 c. View of the area. 



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

 group : Helderberg mouniains. 



Orthis defonnis (n.s.). 



Plate XV. Fig. 3; and Plate X A. Fro. 13, 14. 



Shell suborbicular, lenticular. Ventral valve more convex than the op- 

 posite, most elevated between the centre and beak : beak straight, or 

 often distorted in consequence of having been the point by which the 

 shell was attached. Dorsal valve depressed convex, most elevated near 

 the beak : beak not extending beyond the hinge line. Hinge line 

 straight, equalling about three-fourths the width of the shell. Area 

 broad, flat, sometimes nearly on a plane with the axis of the shell. 

 Foramen closed above, and filled below by the strong cardinal process. 



Subpace marked by prominent rounded striae, which increase by implanta- 

 tion, and are crossed at intervals by distinct subimbricating concentric 

 lines of growth. 



