178 



CYRTOCERAS POSTUMIUS. (N. sp.) 



Description. Shell of medium size ; section elliptical, the transverse 

 diameter being greater than the dorso-ventral in the proportion of about 

 ten to six and a half; nearly uniformly curved, the first two and a half 

 inches on the outside forming a segment of a circle, of which the radius 

 is 2 inches, thence to the apex more rapidly curved. Septa gently concave, 

 three in two and a half lines at about the mid-length. Siphuncle close to 

 the ventral or outer curve, apparently -in contact with the shell, moniliform 

 or expanded into obliquely-depressed globular chambers, each one line in 

 diameter. 



The specimen is 3f inches in length, measured along the outer or ventral 

 side. Transverse diameter at the apierture 10 lines ; dorso-ventral diameter 

 6i lines ; dorso-ventral diameter at the apex 3 lines. The chamber of 

 habitation is not perfect, but, judging from what remains, it must be at 

 least | of an inch in depth. 



Locality and Formation. Cape Smyth, Lake Huron ; Hudson River 

 formation. 



Collector. U. Bell. 



CYRTOCERINA. (N. gen.) 



Generic Character. Fossil Nautilidce having the general characters of 

 Cyrtoceras, but with a large siphuncle on the dorsal side (or on the side 

 of the concave curve). 



The above sub-generic name is proposed for the reception of two 

 remarkable species of Cyrtoceras, which appear to be separated from the 

 main body of the genus by their short thick form and the position of the 

 siphuncle. One of the species occurs in the Black River limestone, and 

 the other in the upper part of the Quebec group. 



CYRTOCERINA TYPICA. (N. sp.) 



Fig. 159. 



Pig. 159. Cytocerina typica. a, dorsal view of a specimen consisting of the septate 

 portion (in part), and showing the cavity of the siphuncle. Owing to the position in 

 which the specimen was drawn, the section, instead of oval, appears to be circular 

 being fore-shortened. The outline figure 6, is the side view. 



Description. This species is founded on a simple specimen, consisting 

 of a portion of the septate part of the shell. Section oval, narrowly 



