4116 PALEONTOLOGY 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 muscuhir 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 towards the centre of the shell. 



Fig. 3.6. 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 podtion and locality. In the Oriskany sandstone : Albany and Scho- 

 harie counties. x 



