93« PALJiONTOLOGY OF NEW-YOKK. 



Renssolirria clliptica ( n. s ). 



Plate XLV. Fia. 4 a, b, c 



Shell elliptical, gibbous or subventricose : valves nearly equally convex ; 

 front rather abruptly rounded ; no trace of a sinus on either valve. 

 Ventral valve arching from the middle towards the lateral margins, and 

 forming longitudinally a semielliptic curve : beak gibbous, closely in- 

 curved and extended over that of the other valve. Dorsal valve most 

 elevated near the middle, rounding laterally, and having a semiellipti- 

 cal outline from the front to the beak, which is incurved. 



Surface marked by fine indistinct radiating striae, which are crossed by 

 obscure concentric lines and faint undulations of growth. 



Fig. 4 a, b, c. Dorsal, profile and front views of the same specimen. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Schoharie county. 



Rensselseria Isevis ( n. s.). 



Plate XL. Fia. 2 a, h. 



Shell broad oval or subquadrate, not sinuate. Ventral valve the more 

 convex, most prominent along the middle and towards the beak, which 

 is pointed and arched, rising above the hinge-line, but not closely in- 

 curved; foramen narrow, extending quite to the apex of the beak. 

 Dorsal valve flat or depressed convex. 



Surface smooth, or only marked by very obscure lines of growth. 



The plano-convex form and smooth surface of this species will at once distinguish 

 it from all its known congeners in the rocks of this State. It is possible there may 

 be very fine obscure radiating strife on perfectly preserved specimens of this species, 

 though the only individual I have yet seen appears to have been smooth. 



Fig. 2 a, h. Dorsal and profile views of a specimen of this species. 



Geological position and locality. lu the shaly limestone of the Lower Helderberg 

 group : Albany county. 



