ORISKANY SANDSTONE. 441 



This species has been found only in casts, or preserving portions of the shell. It 

 differs from R. ohlata in being more deeply sinuate, with coarser and more angular 

 striae. The muscular impression of the ventral valve is proportionally larger and 

 stronger, and the whole shell is more robust. 



Fig. 3 a. A ventral view of a cast. The area of the muscular impression is not suiHciently 

 defined. 



Fig. 3 b. Dorsal view of the same specimen, showing a greater convexity of the valve, and 



a shorter medio-longitudinal septum than the R. oblaLa. 



Fig. 3 c. Front view of the same. 



Fig. 4 a. A larger individual. The specimen is somewhat broken and distorted. 



Fig. 4 6 & c. Dorsal and profile views of the same. 



Geological position and locality. In the Oriskany sandstone : Albany and Scho- 

 harie counties. 



Rliynchonella fitchana. 



Plate GUI. Fio. 1 a, b. 

 Rhifnchonella JUchana : Hall, Regents' Report for 1856, p. 85; Palaeozoic Fossils, 1857, p. 45. 



Shell longitudinally oval or ovate. Dorsal valve very convex : cardinal 

 margin excavated on each side of the beak, for the reception of the 

 dental laminae of the other valve. Ventral valve depressed-convex, 

 most elevated in the umbonial region, flattened towards the lateral 

 margins and depressed in front, forming a faint broad and undefined 

 sinus. 



Surface ornamented by about seventy-five angular plications, which 

 sometimes bifurcate. 

 This species resembles the R. pleiopleura, but is much less distinctly sinuate, and 



with no perceptible mesial fold on the dorsal valve. The muscular impression on the 



ventral valve is small and well defined; being less than in R. ohlata, and less than 



half the size of that in R. pleiopleura, while the plications are stronger than in either 



of those. 



This species, with several others, was received from Alexander Fitch, esquire, of 



Carlisle. 



Fig. 1 a. The dorsal side of the specimen, which preserves a part of the shell. 

 Fig. 1 b. Profile view of the same. 

 Geological position and locality. In the Oriskany sandstone : Carlisle, Schoharie 



county. 



[ PAL^ONTOLOaY III.] 5G 



