176 



Cyrtoceras Huronense. (N. sp.) 



Fig. 158. a, b. 



Description. — Shell rather small, constricted at the aperture ; the 

 ventral outline more curved than the dorsal ; section elliptical, the dorso- 

 ventral diameter being about one-fifth greater than the lateral, at the last 

 chamber, and at the aperture apparently one-third greater. In one spe- 

 cimen the last three septa next the chamber of habitation occupy a space 

 of only one hne, but the next seven occupy six lines, measured on the 

 side. In another specimen there are nine septa in six lines, and in a 

 third, ten septa in seven lines. Siphuncle small, close to the shell on the 

 ventral side. Chamber of habitation of moderate depth. 



One of the specimens, which consists of the cast of the interior of the 

 chamber of habitation, with the last nine septa next thereto, is 16 lines in 

 length, measured along the ventral curve. Dorso-ventral diameter at the 

 smaller extremity 5| lines, lateral 4| lines ; dorso-ventral diameter at the 

 last septum 7^ Hues, lateral 6 lines ; dorso-ventral diameter of the aper- 

 ture 6 Hnes, lateral 4 lines. Depth of the chamber of habitation 

 measured on the side 6 lines, diameter of siphuncle about ^ a line. 



The ventral outline, for 16 lines next to the aperture, is curved to a 

 radius of about 14 lines. The dorsal contour is only slightly concave. 



Locality and Formation. — St. Joseph Island ; Black River or Trenton 

 limestone. 



Collectors. — R. Bell, A. Murray. 



Cyrtoceras Ligarius. (N. sp.) 



Description. — Shell large, gently curved ; section ovate, most obtusely 

 rounded on the dorsal side ; septa eleven in two inches ; chamber of habita- 

 tion moderately deep and apparently with a constriction near the aperture. 

 Siphmicle unknown. 



The specimen is 3 inches in length, curved on the ventral side to a 

 radius of about 4 inches ; but on the dorsal side the septate portion is 

 nearly straight, while the chamber of habitation is slightly curved. Dorso- 

 ventral diameter at the last septum, and also at the aperture, about 20 

 lines. The lateral diameter cannot be clearly ascertained, but it appears 

 to be at the last septum, about 18 lines. Depth of the chamber of habita- 

 tion, about 15 lines. The dorso-ventral diameter at the eleventh septum 

 appears to be about 14 lines. 



This species is very like O. macrostomum (Hall), Pal. N. Y., vol. i, 

 pi. 42, fig. Ibj but is a larger form, and does not taper so rapidly. The 



