370 PALEONTOLOGY OF NEW YORK. 



Selenella qracilis, sp. nov. 



(See page 270, figs. 184-186.) 



Oriskania navicella, 8p. nov. 



PLATE LXXIX, FIGS. 25-27. 

 (See pages 269, 270, figs. 181-183.) 



RensseljEria Cayuga, sp. nov. 



PLATE LXXV. FIGS. 1, 2. 



Shell lenticular, often of large size ; suboval in marginal outline. Valves 

 subequally biconvex, sloping regularly in all directions. Apex of the pedicle- 

 valve scarcely prominent ; umbo not conspicuous, somewhat elevated medially. 

 Divergent cardinal ridges and cardinal slopes well defined. Brachial valve 

 with apex depressed and concealed ; somewhat less convex in the umbonal 

 region than the opposite valve. Surface of both valves covered with a great 

 number of fine, simple, thread-like, rarely duplicating plications, of which 

 from seventy to one hundred may be counted on each valve near the anterior 

 margin. 



Oriskany sandstone. Cayuga, Ontario. 



Begcheria Davidsoni, nom. nov. 



PLATE LXXIX, FIGS. 33-36. 

 (See page 300, fig. 224.) 



