PALEONTOLOGY. 431 



mon, if they were really one and the same, the shell would be preserved 

 on these as well as on the G. cyclops, and the expansions readily detected. 

 Formation and Locality .—In. the limestone of the Upper Helderberg 

 group, near the lower part, at Smith and Price's and at other quarries 

 near Columbus, Ohio. 



Gyroceras seminodosum. 



Pi,ate IV, fig. 5. 

 ■Gyroceras seminodosum Whitf., Ann. N. Y. Acad. Sci., March, 1882, p. 211. 



Shell small, compactly coiled, and consisting, in the specimen used, of a little 

 ■more than two volutions, which increase rather rapidly in diameter with increased 

 age; they are somewhat wider transversely than in a dorso-ventral direction, and 

 are slightly triangularly elliptical in a transverse section ; the greatest transverse 

 ■diameter being very slightly outside of the middle of the dorso-ventral diameter 

 The inner one and a half coils are smooth on the exterior, but the outer volution, 

 for a little more than the larger half, is ornamented by a single series of compara- 

 tively large, transverse, triangularly elliptical nodes on each lateral surface, having 

 the angular side of the node placed anteriorly and the opposite side nearly straight. 

 The nodes are placed at distances from each other about equal to one-half the 

 dorso-ventral diameter of the tube at the node indicated. The septa are not clearly 

 ■defined and cannot be given with certainty; but they appear to be distantly placed 

 ■on the inner portions of the shell, while on the nodose portion they seem to be 

 placed at about half the distance of the nodes apart. The siphuncle has not been 

 observed. The surface of the shell, as seen on a fragment of the substance remain- 

 ing on the dorsum of the outer volution, is marked with rather close, distinct, 

 revolving lines or ridges, crossed by more closely arranged transverse lines, which 

 ■make a shallow retral bend in crossing the back of the shell. 



The specimen is probably an immature shell, but is a distinctly 

 marked species, differing strongly in its form and nodose character from 

 any of those assoc ated with it. It most nearly resembles G.(Hcrcoce- 

 rasf) paucinodus Hall, from the Upper Helderberg group of New York 

 (see Illust. Dev. Foss., pi. 55, figs. 1 and 2), but is less distinctly triangu- 

 lar in a transverse section, that one being widest near the outer portion 

 •of the volution, with a nearly regular sloping surface on the side of the 

 whorl to its junction with the preceding one, while this species is rounded. 

 The form of the nodes is also different — those being situated near the 

 ■dorsal margin. The triangular form of these nodes is peculiar in having 

 the two short sides of the triangle directed forward. It also differs in 

 having a greater number of volutions for a given diameter. 



Formation and Locality.— In limestone of the Upper Helderberg 

 .group, hear Dublin, Ohio. Collected by Mr. Hyatt, of the State Univer- 

 sity, at Columbus, Ohio. 



