OBISKAXY SANESTONE. 448 



Rli}nchoneIIa principalis. 



Plate CVI. Fiq. 4. 

 Rhynchonella principalis : Hall, Regents' Report for 1856, p. 84; Palaeozoic Fossils, 1857, p. 44i 



Shell longitudinally ovate. Dorsal valve unknown. Ventral valve de- 

 pressed convex, forming a low elliptical arch from beak to front, mosfe 

 prominent along the -middle, flattened or somewhat concave near the 

 lateral margins, which are abruptly inflected 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. harrandi; 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 plications. With the knowledge at 

 present possessed, this species may be considered as holding a place intermediate to 

 the very well marked R- speciosa and the equally well marked jR. harrandi. 



Fig. 4. View of the ventral valve, natural size. 



Geological position and locality. In the Oriskany sandstone : Auburn, Cayuga 

 county. From Professor Hopkins. 



Rli} iiclionclla septata ( n. s.). 



Plate GUI. Fio. 2. 



The specimen is a cast of the dorsal valve, which shows, near its margin, iri- 

 distinct marks of a few plications, with the impression of a median septum reaching 

 nearly to the base, which has been extremely thickened towards the beak. The 

 crural processes have been very large and strong, and projecting above these was a 

 strong bilobed process. 



Geological position and locality. In the Oriskany sandstone : Albany county. 



