CEPHALOPODA— ORTHOCHOANITES. 107 



LI. EuTREPHOCERAS Hyatt. 



{Nautilus in part of authors.) 



Highly involute nautilicones, with globose young (nepionic) 

 showing only minute umbilical perforation, and marked by longi- 

 tudinal ridges and transverse bands ; whorls increasing in all diam- 

 eters, changing httle in form in adult, but becoming smooth. 

 Sutures nearly straight. Cretacic. 



136. E. dekayi Morton. (Fig. 1335.) Cretacic. 



F^' Ij35 Xauhlus [Eutrephoceras) dekayi, two views of a small (young) indi- 

 vidual with surface enlarged (right) and a large specimen of var. mortonense with sur- 

 face enlarged (left), all X Yz- (After Meek.) 



Wholly involute in adult ; section of whorl strongly transverse ; 

 cixis extended so as to make the whorls appear auriculate ; septa 

 distant and very concave; siphuncle subcentren; surface with 

 growth lines. In the variety mortonense, the ornamentation of 

 the young is retained. 



Ripleyan of New Jersey, Delaware, Alabama, Minnesota, Arkan- 

 sas; Montanan of Texas, Nebraska, Montana and Canada. 



