430 GKOLOGY OF OHIO. 



shell, below, the peculiar bulging appearance supposed to be characteristic 

 of that genus; but the transverse form and elliptical section, together 

 with the form of the siphuncle and other features, present characters 

 common to the genus Cyrtoceras. It is most nearly related, in general 

 form, to C. Conradi Hall, from the Marcellus shales of New York, but 

 attains a much greater size, has a shorter outer chamber, and is destitute 

 ■of the small lip-like sinus on the ventral side, as seen in that one. The 

 -upper portion of Gomphoceras oviforme Hall, from the limestone of the 

 Marcellus shale, bears considerable resemblance, except in the closing of 

 the aperture, which constitutes a generic difference. 



Formation and Locality. — In the cherty layers of the Upper Helderberg 

 limestone, near Dublin, and at Bellenaris quarry at Georgesville, Franklin 

 ■county, Ohio. 



Genus GYROCERAS DeKoninck. 



Gyroceras Cotumbiense. 



Plate VI, fig. 8. 



■Gyroceras Columbiense Whitf., Ann. N. Y. Acad. Sci., March, 1882, p. 210. 



Shell of about a medium size, often attaining a diameter across the disk of about 

 six inches, although the majority of the specimens seen will not measure more' 

 than five. The shell is closely coiled, the volutions being in absolute contact and 

 about one and a half or two in number. Volutions nearly circular in a transverse 

 ■section, being a very little greater in the lateral direction than in the dorso-ventral, 

 and the back of the volution barely perceptibly flattened on the outer portion of the 

 larger one, but not perceptibly so on the inner portions. Septa deeply concave and 

 distantly arranged ; the chambers measuring about half an inch each, on the outer 

 two-thirds of the body volution of a specimen where the vertical, or largest, di- 

 ameter of the disk is five inches. Position of the siphuncle not absolutely deter- 

 mined. Surface of the shell unknown. 



All the individuals of this species observed are internal casts, and 

 ■occur in a rather rotten limestone, under conditions very unfavorable for 

 the preservation of the shelly substance; consequently the surface char- 

 acters have not been observed. It is an abundant species, but owing to 

 the conditions of preservation, is not often found in collections. It will 

 be readily distinguished from the other described species by the closely 

 ■coiled volutions and the nearly circular section. It is perhaps more 

 nearly related to G. cyciops Hall, 15th Rept. N. Y. State Cab. Nat. Hist., 

 than to any other described species; but it differs from that one in its 

 smaller size, and more rapidly increasing as well as more closely coiled 

 volutions, and does not appear to have been provided with the broadly 

 expanding and foliated varices which are so characteristic of that species- 

 It might be objected, that as the shell of this species is unknown, the 

 •determination of the absence of these foliated expansions is not well 

 authenticated; but it may be answered, that as the two species are asso- 

 ciated in the same layers in the quarries where they are both rather com- 



