162 



Fig. 146. 



Fig. 146. Cyrtoceras Lysander, a, Side view of a fragment ; 6, d, transverse 

 sections, showing some difference in form ; c, a portion of the 

 ventral side ground down to the siphuncle. 



with fine engirdling undulations, 3 or 4 in one line, so obscurely developed 

 that, on a superficial glance, the shell seems to be somewhat smooth. 



A fragment of this shell 18 lines in length tapers about | of a line. 

 The relative proportion of the dorso-ventral and lateral diameters of the 

 section is somewhat variable. The following are the measurements of the 

 sections of several fragments apparently belonging to different individuals : 

 9, 7 J ; 9, 7 ; 8, 6J ; 8i, 6. In these figures the larger number is the 

 lateral diameter, and the smaller the dorso-ventral. In some fragments 

 the ventral side is narrowly rounded along the middle, but in others it is 

 like the dorsal side gently convex. 



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

 group. 



Collector. R. Bell. 



CYRTOCERAS ORODES. (N. sp.) 



Description. Section nearly circular, the dorso-ventral diameter 

 slightly greater than the lateral. Aperture 15 lines in diameter ; shell 

 at 9 lines from the aperture, 11 lines in diameter ; depth of chamber of 

 habitation 9 lines. The septate portion of the specimen is 21 lines in 

 length measured on the ventral side, and in that distance there are 12 

 septa. The specimen is so gently curved that in a length of 30 lines the 

 arch formed by the ventral outline is only 5 lines in height in the middle. 



This shell differs from C. Orestes in being more gently curved, and in 

 having the aperture expanded. 



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

 Middle Silurian. 



Collector. J&. Billings. 



