ORISKANY SANDSTONE. 
439 
Rliynchonella oMata. 
Plate CII. Fig. 1 ? & 2 a - d. 
Rhynchonella oblata : Hall, Regents’Report of 1856, p. 86; Palaeozoic Fossils, 1857, p. 46. 
Shell subcircular, somewhat compressed. Dorsal valve the larger, de¬ 
pressed convex, declining with a gentle curve towards the lateral 
margins, rising in front into a broad round undefined mesial fold : beak 
somewhat incurved. Ventral valve much compressed, depressed convex 
in the middle and umbonial regions, and depressed into a broad shallow 
undefined sinus in front. 
Surface marked by seventy-five to eighty coarse strise, which occasionally 
bifurcate, and of which twelve to fourteen or more mark the mesial 
fold and sinus. 
The specimen fig. 1, which is referred with doubt to this species, preserves a part 
of the shell : the other specimens are casts. The muscular area of the ventral valve 
is comparatively small, and the space for the adductors quite narrow. The ramifying 
vascular impressions are beautifully preserved in a single specimen, radiating from 
the muscular area and extending to the cardinal line, where they are strongly 
marked. In the dorsal valve the medio-longitudinal septum extends from the beak 
nearly halfway to the base of the shell, the cast sometimes showing the marks of 
muscular impressions. The impressions of the radiating strise are preserved on the 
lower half of the casts. 
Fig. 1. A young individual, retaining a part of the shell on the dorsal valve. 
Fig. 2 a. Front view, showing the broad shallow sinus. 
Fig. 2 b . The ventral side of another specimen, showing the muscular area and the ramifying 
vascular impressions. ( The latter are represented in lines too sharply defined : 
the two sides are not connected by a sharp line, as shown in the figure ; and 
their extension towards the front of the shell is in shallow depressions, which 
gradually become obsolete.) 
Fig. 2 c & d. Dorsal and cardinal views of the same specimen. 
Geological position and locality. In the Oriskany sandstone : Albany and Scho¬ 
harie counties. 
