161 



CEPHALOPODA. 



ORTHOCERAS DARWINI. (N. sp.) 



Description. The only specimen of this species collected is 3-| inches 

 in length ; section apparently transversely oval ; lateral diameter at the 

 larger extremity about 2 inches, at the mid-length Ij inches, and at the 

 smaller extremity 1 inch. The dorso-ventral diameter at the smaller 

 extremity is 9 lines, but at the larger, in consequence of the imperfection 

 of the specimen, it cannot be ascertained. In 2^ inches of the length 

 there are 19 septa. These appear to be nearly flat or only gently con- 

 cave. The siphuncle appears to be moniliform, 2 lines in thickness, and 

 with its centre 6 lines from the dorsal and 3 lines from the ventral margin. 

 The surface of the cast is longitudinally sulcated by obscure furrows about 

 1 line apart, showing that the shell itself must be marked in a similar 

 manner. The specimen is slightly curved. 



It is not certain to what extent the transversely ovate form of the sec- 

 tion of this species may be due to compression. From the fact that the 

 septa do not appear to be distorted, I think the measurements above 

 given indicate the natural proportions. 



Locality and Formation. New Hope. In the Guelph formation; 

 Middle Silurian. 



Collector. E. Billings. 



ORTHOCERAS SELWINI. (N. sp.) 



Description. This specimen is 3 inches in length ; lateral diameter at 

 the larger extremity 14 lines ; at the smaller 9 lines ; the dorso-ventral 

 diameter seems to be a little less, but one side of the specimen is imper- 

 fect. In a length of 3 inches there are 24 septa. The siphuncle appears 

 to be moniliform ; the inflations between the septa discoid, and 4 lines in 

 diameter ; the centre of the siphuncle 3 lines from the ventral margin. 



Locality and Formation. Gait. In the Guelph formation; Middle 

 Silurian. 



Collector. Si. Bell. 



CYRTOCERAS LYSANDER. (N. sp.) 



Description. Shell elongate, slightly curved, and very gradually 

 tapering. Section transversely ovate ; septa varying from moderately 

 to rather strongly concave, from 15 to 20 in one inch ; siphuncle about a 

 line in diameter, and almost in contact with the shell on the ventral side ; 

 chamber of habitation apparently more than 1 inch in depth ; surface 



