FOSSILS OF THE CLINTON GROUP. 543 



the siphuncle is unknown. The shell is about .2 ram. thick, and, while the 

 surface is practically smooth, a trace of cross-striation owing to irregular- 

 ity of growth is seen in some specimens. This shows how closely re- 

 lated must be the subgenera Eu-Orthoceras and Cycloceras. The vertical 

 linear marking, called a carina, is seen on one side in some specimens. 

 Until the siphuncle is better known, these specimens will be best re- 

 ferred to the present variety. , 



Orthoceras (Eu-Orthoceras) Hanoverense, Foerste. 



( Plate 32, Fig. 6 ; Plate 35, Fig. 5.) 



This species was described from Hanover, Indiana, in the Proc. 

 Boston Soc. Nat. Hist., 1889. It may well be questioned if all the inter- 

 esting and peculiar structures discovered in the type specimen will be 

 found characteristic of the species. From typical forms of Orthoceras 

 ignotum it can always be distinguished, but whether the greater num- 

 ber of septa and the somewhat narrower, and at a corresponding age 

 more moderately annulated siphuncle will always serve to distinguish 

 this form from the species O. erraticum remains to be determined. 



A species from Hanover, Indiana, shows the numerous septa, but 

 the cast of the chambers has no obliquely impressed line as in the type ; 

 it did not show the siphuncle, its shell surface was smooth. (Plate 35, 

 Fig. 5.) A second specimen from the Soldiers' Home in the cabinet of 

 Mr. Geo. Caswell, and a third in the collection of Dr. Chas. Welch, from 

 Todd's Fork, possess similar close septa, but no obliquely impressed line. 

 For the present at least these forms will be placed under O. Hanoverense. 



Orthoceras (Eu-Ortkoceras!) virgulatum, Hall? 



( Plate 32, Fig. 5 : Plate 35, Fig. 3.) 



This very doubtful form, described from the Soldiers' Home, (Proc. 

 Boston Soc. Nat. Hist., 1889), is characterized by a very low rate of in- 

 crease in diameter, rather distant septa, and a very attenuated cylindrical 

 siphuncle. O. inceptum seems never to have the septa so far distant in 

 the broader parts of the specimens, nor the siphuncle so regularly at- 

 tenuated as this specimen. A form with somewhat broader siphuncle 

 occurs in the collection of Mr. Geo. Caswell from Soldiers' Home. Plate 

 35, Fig. 3. 



Orthoceras {Cycloceras) inceptum, Foerste. 



(Plate 25, Figs. 1 a, b c.) 



Typical specimens of this species are rather common in the Beaver- 

 town marl at the top of the Clinton Group at Huffman's Quarry (Bull. 

 Denison Univ. Vol. I), and in the corresponding marl at Geo. Young's 

 quarry, west of Soldiers' Home. At both localities the specimens are 

 always in the form of internal casts. They are quite small, the largest 

 specimens attaining a diameter of only 5.5 mm. The position of the 



