64 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



CLYMENIA ERATO ( n. s.). 10 I' I 

 Shell discoid. Volutions about three, besides the nucleus : centre 

 depressed below the plane of the outer volution, which is mo- 

 derately convex on the side, and embraces about one-third the 

 width of the penultimate volution. Outer volution obtusely angu- 

 lar on the dorso-lateral margins, with a distinct revolving groove 

 on the side about one-third the width from the dorsal margin . 

 this groove, upon the inner volution, is visible within the suture 

 line. 

 Surface marked by fine equal strise, which are directed a little 

 backwards from the ventral side of the volution, are fainter on 

 the middle of the side, and, turning a little into the groove, are 

 abruptly bent forward beyond it, and, upon the middle of the 

 dorsal lobe, make a very sharp curve, turning backwards and 

 reaching the dorso-lateral angle, which is slightly truncate (and, 

 in crushed specimens, is marked by a shallow groove). The back 

 is somewhat liattened : septa undetermined. 



This species, in the largest specimens seen, is nearly two inches in dia- 

 meter ; and the outer volution, when flattened, is five-eighths of an inch 

 from the ventral to the dorsal side. It differs from C. complanata, in having 

 a lesser number and more robust volutions, the penultimate one of which is 

 more embraced within the outer one ; in the form of aperture, and conspi- 

 cuously in the direction of the surface stri?e. 



Geological formation and locality. In a compact calcareous band at the 

 top of the Hamilton group at Fall brook, Geneseo, and at Paterson's creek, 

 Moscow, N.Y. 



GENUS TROCHOCERAS^ (Barrande, Hall). 



TROCHOCERAS DISCOIDEUM ( n. s.). 

 Shell subdiscoid, making three or four volutions, broadly umbili- 

 cate on the lower side. Volutions contiguous, slender, gradually 

 enlarging from the apex : peristome somewhat abruptly expanded ; 



* The Gemis Trochoceras was proposed almost simultaneously by M.Barrandb 

 and myself for fossil species generically similar, and witliout any concert of action, or 

 of either being aware of the conclusions of the other. The name proposed by me was 

 printed in the second volume of the Pahneontology of New-York in 1850, although the 

 volume was not issued till 1852; and it was only after this that I became aware that 

 M. Barrande had published a Genus Trochoceras. 



[ September, 



