84 [ SXNATK 



Rhynchonella barrandi. 



Rhynchonella principalis. 



Pal. N.Y. Vol. iii, pi. 106, f. 4. 



Shfxl large, longitudinally ovate : dorsal valve unknown : ventral 

 valve depressed-convex, forming a low elliptical arch from beak 

 to front, most prominent along the middle, flattened or some- 

 what concave near the lateral margins which are abruptly de- 

 flected upwards towards the opposite valve ; beak somewhat 

 prominent and moderately incurved ; front slightly concave, 

 but not distinctly sinuate. Surface ornamented by about eighty 

 regular rounded plications, which occasionally bifurcate, and 

 are crossed by indistinct lines of growth. 



This species is closely related to R. barrandi ; and having but a single 

 ventral valve, I cannot readily decide how far it may differ in its entire 

 characters. The casts of the preceding species are all proportionally broader 

 when not compressed, have a more distinct sinus in front, and fewer plica- 

 tions. With the knowledge at present possessed, this species may be con- 

 sidered as holding a place intermediate between the very well-marked R. 

 speciosa, and the equally well-marked R. barrandi. 



Geological position and Zocatoy.,Oriskany sandstone, Auburn ( N.Y.). 



