4«4 PALEONTOLOGY OF NEW-YORK. 



Rensselivria ciiiiilH>rlaii(li)C. 



Plate CVIII. Fig. I a - c. 

 Mtganlerit cumberlanditt : Hall, Regents' Report for 185G, p. 101; Palseozoic Fossils, 1857, p. 61. 



Shell elliptical : valves nearly equal, somewhat acutely rounded in front ; 

 no trace of a sinus in either valve ; lateral margins abruptly inflected. 

 Ventral valve rounded and most convex along the middle, sometimes 

 becoming angular towards the beak, sloping laterally and forming a 

 broad semielliptical curve from front to beak, a little more gibbous 

 above than below the centre : beak prominent, slightly arched ; fora- 

 men terminal, small when the deltidial pieces are present, large and 

 triangular when these pieces are removed. Dorsal valve depressed- 

 convex, a little smaller than the other : beak scarcely incurved. 



ScRFACB apparently smooth, or marked by obscure concentric lines and 

 faint wrinkles of growth, and, near the margin, by strong radiating 

 striae. 



This is a very distinct species, and may be distinguished from R. suessana, some 

 varieties of which it most resembles, by its more elongate form and the more promi- 

 nent beak of the ventral valve : the cardinal margin of the ventral valve, on each 

 side of the beak, is also more extended, and the margins of the valves are never so 

 abruptly incurved. Some specimens, from interrupted growth, present a thickened 

 Imbricating lateral and frontal margin. 



Fig. 1 a, b, c. Ventral, dorsal and profile views of an entire specimen. 



Fig. 1 d, e,f. Ventral, dorsal and profile views of an imperfect specimen, the dorsal view 

 showing the triangular foramen which results from the removal of the deltidial 

 plates. ( These three figures were placed upon the stone before perfect specimens 

 were obtained.) 



Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 



