416 
PALAEONTOLOGY OF NEW-YORK. 
The ventral valve has not been positively identified in its external or 
internal characters. The interior of the dorsal valve is gently concave 
over the greater part of its area, and, towards the margin, is suddenly 
bent upwards or outwards, the line of bending being distinctly defined at 
about a quarter of an inch from the margin in front, in shells of ordinary 
size; the distance at the sides, and towards the cardinal angles, being 
somewhat less. 
The cardinal process is bifid at the extremity uniting in one below; 
being continued laterally in an oblique and gradually curving direction, 
limiting the cardinal muscular impression by a low crest, and continued 
from the centre in a more prominent median ridge to the commencement 
of the adductor muscles, or about one-fourth the entire length of the shell, 
where it is flattened, and rises again below this point The imprints of the 
cardinal and adductor muscles are not strongly defined, though the places 
of the latter are indicated in their outer limits by a low ridge on each 
side parallel to the median one. 
The entire interior of the shell is finely punctate or striato-punctate. 
The specimens, which can be referred with certainty to this species, are impres¬ 
sions of the exterior of the dorsal valve, and impressions of the interior of the same 
valve. It is distinguished from the other species by its comparatively more elongate 
form. The interior is marked by a more slender cardinal process and fainter median 
lines, while the muscular and vascular impressions are much less strongly defined. 
In the absence of well-determined exterior characters, and of the interior of the 
ventral valve, we may rely on the interior of the dorsal for characterizing the 
species. 
Fig. 2 a ( the specimen referred with doubt to this Species). The exterior of a ventral valve, 
in which the shell is partially exfoliated. 
Fig. 3 a. The imprint made by the interior of the dorsal valve of a small individual, showing 
the cavities made by the bifurcating cardinal process, the impressions of the 
median crest, and the low ridges towai’ds the centre of the shell. 
Fig. 3 h. The impression of a larger ventral valve of this species, showing the Same features 
as the preceding, the crenulated hinge-line, and the abruptly recurved outer 
margin. 
Geological 'position and locality. In the Oriskany sandstone : Albany and Scho¬ 
harie counties. 
