86 [Senate 



Rhynchonella oblata. 



Pal. N.Y. Vol. iii, pi. 102, f. 2. 



Shell subcircular, somewhat compressed : dorsal valve the larger, 

 depressed-convex, declining with a gentle curve toAvards the 

 lateral margins, rising slightly in front into a broad round un- 

 defined mesial fold ; beak somewhat incurved : ventral valve 

 much compressed, slightly convex in the umbonial region, de- 

 pressed into a broad shallow undefined sinus in front. Surface 

 marked by seventy-five to eighty coarse stria3 which occasional- 

 ly bifurcate. 

 Internal casts of this species only have been observed, hut its general 



form appears to he sufficient to distinguish it from any of the preceding 



species. 



Geological positio?i and locality. Oriskany sandstone, Carlisle ( N.Y.) . 



Rhynchonella PLEIOPLEURA. 



Pat. N.Y. Vol. iii, pi. 102, f. 3 a - c and 4 a - e. 



Atrypa pleiopleura, Conrad : An. Eeport Pal. N.Y. p. 55. 



Shell transversely oval : dorsal valve the larger, somewhat gib- 

 bous, having a round or sloping mesial fold; beak incurved; 

 cardinal border excavated on each side of the beak, for the 

 reception of the dental laminEe of the opposite valve :' ventral 

 valve nearly flat, most elevated near the beak, having a some- 

 what deep, broad, rounded sinus near the front margin, which 

 is prolonged into a rounded or subtriangular projection. Surface 

 ornamented by from sixty-four to seventy rather angular bi- 

 furcating strise or plications. 



This shell has been found in casts only : it differs from the last species 

 in being more gibbous, more distinctly sinuate, the striae stronger, and 

 impressions of the adductor muscles larger and more prominent. 



Geological positio7i and locality. Oriskany sandstone, Schoharie. 



