88 PROCEEDINGS OF THE ACADEMY OP 



tion at the same point ; curving gracefully backward as they cross 

 the sides, and forward as the}' pass from the sides to the flattened 

 periphery, in crossing wliich the}' again make another, but stronger, 

 backward curve. Body chamber large, or occupying more than 

 half the outer volution. Surface (of cast) ornamented by small 

 transverse ridges, of which about thirty may l^e counted to a side 

 of each volution, the outer half only of which they occupy, without 

 passing over or upon the periphery; while on the inner volutions 

 they are sometimes so short as to assume the aspect of trans- 

 versely elongated nodes. Siphuncle, aperture, and finer surface 

 markings unknown. 



Greatest diameter across the disc of a specimen with a part of 

 the outer volution broken away, about nine inches ; dorso-ventral 

 diameter of outer volution at the point where it is broken olfj 

 3.63 inches ; thickness, or transverse diameter, of same at same 

 point, about 3.90 inches. 



Owing to the fact that the only two specimens of this species I 

 have seen are both in such a condition as to show clearly only 

 one side (the upper side of it is a Trochoceras), I am in some little 

 doubt whether it is a Oyroceras or a Trochoceras. From the 

 depth of the concavity of this side, however, I can scarcely question 

 that the volutions are really coiled in the same plane, as in Gyro- 

 ceras and Nautilus. The contiguous character of its volutions 

 (excepting apparently the last one, near the aperture) is, how- 

 ever, rather against its being a Gyroceras, though the inner turns 

 are sometimes in contact in species apparently belonging to that 

 genus. If the last turn reallj' does become free, as seems to be 

 the case, this character would be equally against the probability 

 of its being a Nautilus; but as the specimens are not in a condi- 

 tion to quite remove all doubts on this point, it is barely possible 

 that this shell may be found to belong to some of the sections of 

 that group, though I can scarcely think so. 



I know of no described species of Gyroceras so nearly allied to 

 this specificall}', as to require a close comparison. 



Locality and position. Delaware, Ohio, and in Marion County 

 of the same State. Coruiferous limestone of the UpiDcr Helderberg 

 Series (Devonian). 



[June 6, 



