439 
PALAEONTOLOGY OF NEW-YORK. 
Leptoceelia dichotomy (n. s.). 
Plate CIII B. Fig. B a, b, c. 
Shell oval ovate, concavo-convex. Ventral valve arcuate, strongly convex, 
or approaching to subcarinate in the middle and abruptly sloping at the 
sides : beak incurved. Dorsal valve concave, more abruptly depressed 
in the centre, and flattened on the cardino-lateral margins. 
Surface marked by dichotomizing plications ; the central one of the 
dorsal valve becoming tripartite, and the three lateral ones, which are 
simple at their origin, bifurcating and making six at the margin of the 
shell : on the ventral valve there are two smaller plications in the 
centre, and four dichotomizing ones on each side; concentrically 
marked by a few imbricating lines of growth. 
This species resembles L. con cava of the Lower Helderberg rocks, but is much 
larger, and the manner of bifurcation of the plications is very distinctive. The 
depressed space in the centre of the dorsal valve is not so abrupt, and the flattened 
portion on the dorso-lateral margins is proportionally much narrower than in the 
species from the limestone. 
Fig. 3 a. Dorsal view of tlie specimen. 
Fig. 3 b. Ventral view of the same. 
Fig. 3 c. Front view, showing the outline, the depression of the dorsal valve, and 
the incurved beak. 
Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 
Fig. 1. The ventral valve of L. flabell-ites, showing the dental processes and the muscular impression. 
Fig. 2. The dorsal valve, showing the cardinal processes, dental fossets, muscular impressions, etc. 
Fig. 3. Dorsal view of L. fimbriata. 
