532 Contributions to Invertebrate Palaeontology. 



exceeding the dorso-veutral diameter of the lower end ; margin simple, so far 

 as can be determined from any of the specimens, showing only a broad, shallow 

 sinuosity on each side. Septa somewhat closely arranged and deeply concave, 

 but slightly increasing in distance in the upper part, the average length of 

 the chambers being about one-tenth of an inch, but somewhat more crowded 

 just below the outer one. Siphuncle of moderate size, situated a little within 

 the dorsal surface, and very slightly expanded within the chambers. Surface 

 of the shell marked only by transverse lines of growth parallel to the margin 

 of the aperture. 



The shells are moderately abundant, and show slight variations 

 in form among individuals, especially in the rate of increase in 

 dimensions or in the regularity of the expansion, as well as in the 

 comparative distance between the septa ; a single individual show- 

 ing a much greater distance between them in the upper part of its 

 length. The shell would probably be considered by some as belong- 

 ing to the genus Oncoceras, as the decrease in diameter in the upper 

 part of the outer chamber gives to the 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 com- 

 mon 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 resem- 

 blance, 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 Co., Ohio. 



Genus GYROCERAS DeKoninck. 



Gyroceras Coluin1)ieiise. 



Plate X, fig. S. 



Gi/roceras 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 si)ecimens 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 



