CEPHALOPODA— CYRTOCHOANITES. 1 1 5 



Fig. 1349. Gigantoceras inelegans, ^s- (After Meek, Pal. Ohio.) 



annuli; septa often double, an interspace near siphuncle, solid 

 near shell. Ordovicic-Carbonic. 



150. A. bigsbyi Stokes. (Fig. 1350.) Ordovicic. 

 Septa deeply concave; siphuncle large; siphonal bead occupying 



fully two thirds of diameter of shell. 



Stones River and Black River beds of Minnesota, Cincinnati 

 region and Tennessee; Trenton of New York, Minnesota and 

 Tennessee. 



151. A. tenuifilum Hall. (Fig. 135 1.) Ordovicic. 

 Siphuncle very large ; septa crowded conspicuously, double, with 



large interspaces; concavity much less than in preceding. 

 Black River of New York. 



152. A. remotiseptum Hall. Ordovicic. 

 Large, cylindrical, gradually tapering ; septa moderately concave ; 



widely separated (by half the diameter of tube) ; siphuncle excen- 

 tric, moderately swelling between septa. 



Lowville and Trenton of New York; Trenton of Minnesota. 



