4 le PALEONTOLOGY OF NEW-YORK. 



Rli}iichoiiclla raiiisayi ( n. s.)- 



Plate CI A. Fio. 7 & 8 a, 6. 



Shell longitudinally ovate, valves equally convex, gibbous towards the 

 umbones and declining towards the front and sides, symmetrically 

 rounded in front, with moderate sinus and elevation below the middle. 

 Ventral valve convex in the middle and gradually tapering to the beak, 

 which is small and neatly incurved over the umbo of the opposite valve, 

 the truncated extremity being on a plane with the axis of the shell ; 

 the margins on each side, below the beak, slightly auriculate. Dorsal 

 valve most convex at the first third from the beak : margins on each 

 side, below the beak, moderately sinuous. 



Surface marked by thirty-six to forty or more slender rounded plications 

 on each valve, about fourteen of which, in the centre and near the 

 front, become a little larger and more prominent than the others on 

 the dorsal valve, while an equal number on the ventral valve are just 

 perceptibly depressed. 



The cast shows a defined longitudinally oval muscular impression on 

 the ventral side ; while the dorsal side shows the mark of the median 

 septum, and the cavities made by the slender crural processes. 



This species is quite distinct from any other known to me in the Lower Helder- 

 berg and Oriskany sandstone ; being less gibbous than any one of the same size, 

 while the mesial elevation is scarcely perceptible, except in the greater size and 

 slightly greater prominence of the plications. 



Fig. 7. View of the dorsal side of the specimen. 



Fig. 8 a, b. Ventral and dorsal views of the cast of this species. 



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



