﻿Cephalopoda of the Cincinnati Group. 



243 



KEY TO SPECIES. 



Surface marked by transverse striae. 



Septa concave. 



Siphuncle very large. 



Siphuncle marginal, obliquely annulated. 



E. proteiforme, i. 



E. annulatum, 2. 



E. magniventrum, 3. 



E. approximatum, 4. 



Siphuncle sub-central, with elevations at the septa. E. sub-cenirale, 5. 



I. E. PROTEI FORME, Hall. 1 847. 



(Pal. N. Y., I, p. 208. Plates 45 to 50 and 53.) 



General form cylindrico-conical, more or less elongated, often com- 

 pressed, tapering unequally ; young specimens terminating in an acute point; 

 surface marked by distinct transverse stria, usually like narrow, sub-imbri- 

 cating bands, one edge well defined and more elevated than the other, 

 more or less distinctly striated longitudinally : striae varying from extreme 

 tenuity to distinct, elevated thread-like lines; section circular ; septa distant 

 one-fifth to one-fourth of the diameter of shell ; siphuncle eccentric or sub- 

 marginal. 



Locality : Cincinnati. 



This species is well named, for the forms are endless. As none of 

 them seem to be well defined, however, all running together, none of the 

 supposed and described varieties are here considered separately. 



Cylindrical, gradually tapering toward apex; annulations broad, 

 rounded, equal to depressed interspaces, distant one-fifth diameter of the 

 tube and slightly arched ; septa deeply concave, bending more abruptly 

 backward just before reaching the siphuncle, and more approximate than 

 the annulations; siphuncle large, sub-dorsal, with smooth embryo tube.; 

 section circular ; surface markings unknown. 



Locality : 



Chiefly recognized by the deeply concave septa, a character not found 

 in any other of our species. 



Elongated, very gradually tapering ; sij?huncle very large, occupying 

 three-fifths of diameter of the shell ; septa very convex ; distant one-eighth 

 the diameter of the shell. 



Locality : Cincinnati. 



2. E. ANNULATUM, Hall. 1847. 



(Pal. N. Y., I, p. 207. PI. 44, figs. 1 a b.) 



3. E. MAGNIVENTRUM, Hall. 1847. 



(Pal. N. Y., I, p. 218. PI. 53, figs, i a to e.) 



