86 [Senate 



RUYNCHONELLA OBLATA. 

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



Shell subcircular, somewhat compressed : dorsal valve the larger, 

 depressed-convex, declining with a gentle curve towards the 

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

 defined mesial fold; beak somewhat incurved : ventrq^l valve 

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

 pressed Mo a broad shallow undefined sinus in front. Surface 

 marked l:)y seventy-five to eighty coarse strias which occasional- 

 ly bifurcate. 

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



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



species. 



Geological position and. locality. Oriskany sandstone, Carlisle ( N.Y.). 



Rhynchonella PLEIOPLEURA. 



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



Atrypa pleiopleura, Conrad : An. Report Pal.N.T. 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 tlie 

 reception of the dental laminse 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 sevenly rather angular bi- 

 furcating stride or plications. 



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

 in being more gibbous, more distinctly sinuate, the stria; stronger, and 

 impressions of the adductor musclos larger and more prominent. 



Geological position and locality. OriekaDy Eandstone, Schoharie. 



