426 GEOLOGY OF OHIJ. 



the one from the Hamilton group of N. Y., figured by Prof. Hall (PaL 

 N. Y., Illust. Dev. Foss., PI. 43, fig. 14), in the rate of increase in the 

 diameter, and in the form and relative strength of the annulations than 

 with the original specimens to which the name was first applied, or to 

 most of those figured under the same name on the same plate. The 

 specimen from Ohio figured on PI. 41, fig. 9, Illust. Dev. Foss., Pal. N. 

 Y., under the name O. Thoas, is identical with the one here described, 

 but does not retain the shell nor show surface markings, but corresponds 

 in the form of the annulations and in its slight curvature and rate of in- 

 crease in diameter, in which particulars it differs materially from those 

 from New York, given on the same plate. It is barely possible the Ohio 

 specimens may represent a species distinct from any of those from New 

 York, but it seems totally impossible to detect characters sufficient to 

 distinguish it as such. O. siibulatum Hall, from the Marcellus shell is a 

 very closely allied if not identical form. 



Formation and Locality. — In the cherty layers of the Upper Helder- 

 berg group, near Dublin; and in the limestone of the same formation 

 near Delaware and Columbus, Ohio. 



CEPHALOPODA. 

 Genus TREMATOCERAS Wh'.tf. 



Ann. N. Y. Acad. Sci., March, ]S82, p. 205. 



A straight, obconical, cephalopodous shell, presenting the characteristics of 

 an Orthoceras, so far as the appearance of the tube, septa and siphuncle is con- 

 cerned; but with the additional feature of a line of elongated, raised tubercles 

 along one side of the shell, which have formed perforations at certain stages of 

 growth, probably confined to the outer chamber as openings, which were closed as 

 the animal extended the shell, and before the septa opposite them were formed- 

 Type, T. Ohioense. 



The shell for which the above generic name is proposed offers an 

 entirely novel feature among the Orthoceratidse. The line of nodes seen 

 on the cast of the shell is entirely different from anything pertaining to 

 the ornamentation of the shell, and presents the same appearance as 

 would the partially filled perforations of a Haliotis, or like those shown 

 on the back of species of Bucania, and those on which the genus 

 Trcmanotus was founded ; neither is it a feature at all dependent upon 

 the position of the siphon or directly connected with it ; for in the speci- 

 men used the siphon is slightly eccentric, on the opposite side of the 

 tube from the nodes. Its position would thus indicate that it was a fea- 

 ture pertaining to the dorsal lip of the shell, corresponding to the sinus 

 seen in the lip of man}?- other genera. Taking this view of it, it would 

 appear to indicate the existence of a deep, narrow notch, with raised 

 margins, in the lip of the shell at stated periods, be3 r ond which the shell 

 was again united for a time, leaving a perforation to be closed by a de- 

 posit of shell from the mantle as it approached the lower part of the 



