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 1\ 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 monihform, 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 longitudmally sulcated by obscure furrows about 

 1 hne 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 Unes ; 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 monihform ; the inflations between the septa discoid, and 4 lines in 

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



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

 Silurian. 



Collector.— R. Bell. 



Cyrtoceras Lysander. (N. sp.) 



Description. — Shell elongate, shghtly 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 



