174 
PALAEONTOLOGY OF NEW-YORK. 
Ortliis pcduncularis (n. s.). 
Plate XIII. Fig. 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 fiuely 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 b. 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. 
Ortliis deformis (n.s). 
Plate XV. Fig. 3 ; and Plate X A. Fig. 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. 
Surface marked by prominent rounded striae, which increase by implanta¬ 
tion, and are crossed at intervals by distinct subimbricating concentric 
lines of growth. 
