3S8 PALAEONTOLOGY OF NEW-YORK. 



and fold, partially depressed or elevated, and smaller than the others. 

 The shell has been marked by elevated thread-like concentric stris9. 



Tho specimens described are essentially casts, the shell being partially pre- 

 sei'ved ou one of them. The species diflers from all the other I'hynchouclloid forms 

 of the limestone, in the broad scarcely defined sinus, which is not abruptly eleva- 

 ted in front ; and in the undefined margins of the fold, which arc marked on the 

 slope by a less strongly raised plication. The beak is also more extended than in 

 the other species. 



lu casts of the ventral valve, there is no important distinction between this and 

 other forms in regard to the dental plates, etc. ; but I am induced to believe that 

 investigation upon more extensive material will prove the characters of the dorsal 

 valve to be so far distinct as to require generic separation. 



Geological formation and localities. In the Corniferous limestone at Sandusky, 

 and near C!olumbus, Ohio. 



Rli}iicIionelIa ? ( Stenocisnia ? ) royana (n. s.). 



PLATE LIV. 



Shell ovate, compressed ; beaks nearly equal : valves almost equally 

 convex above ; the dorsal valve continuing in a pretty regular con- 

 vexity, and the ventral valve depressed iu a broad undefined sinus. 

 The surface is marked by about tvpenty-four or more slender plications 

 on the margin, the three or four central ones on the dorsal valve bifur- 

 cating once above the middle of the shell, and some of them again below 

 the middle : the same feature is more or less characteristic of the ven- 

 tral side. The plications upon the sides of the shell are simple and 

 become obsolete on the cardinal slopes, which are marked only by con- 

 centric striae. When perfect, the entire surface has been marked by fine 

 concentric striae. 



The hinge-line presents obscure indications of an area on the ventral valve, 

 and the species is unlike anything else known iu the formation. It cannot be 

 referred Avith certainty to any known genus. It is extremely rare, and but a single 

 individual has been found. 



Geological formation a7id locality. In the Corniferous limestone, north of Leroy, 

 New- York. 



