338 
PALAEONTOLOGY OE NEW-YORK. 
and fold, partially depressed or elevated, and smaller than the others. 
The shell has been marked by elevated thread-like concentric striae. 
The specimens described are essentially casts, the shell being partially pre¬ 
served on one of them. The species differs from all the other rhynchonelloid 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 are marked on the 
slope by a less strongly raised plication. The beak is also more extended than in 
the other species. 
In 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 Columbus, Ohio. 
Rliynchonella ? (Stenocisma ?) royana (n. s.). 
PLATE LIY. 
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 twenty-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 in the formation. It cannot be 
referred with certainty to any known genus. It is extremely rare, and but a single 
individual has been found. 
Geological formation and locality. In the Corniferous limestone, north of Leroy, 
New-York. 
