ART. 5 A NEW NAUTILOID CEPHALOPOD REESIDE. S 



groups of specimens of the same age and restricted geographic distri- 

 bution and differ between the respective groups. It is likely that if 

 complete and well-preserved shells were available numerous other 

 differences would be found, but it seems desirable to distinguish the 

 various groups that can be recognized now even though some of them 

 are difficult to separate on the basis of such details as are commonly 

 preserved. 



EUTREPHOCERAS SLOANI, new species. 



Shell of medium size, the largest diameter of the type specimen 

 preserved being about 140 mm. (the complete shell must have been 



Fig. 1. — Cross section of whorl of Eutrephoceras sloani Reeside at oiameter of 

 140 MM., natural size. a. Suture of Enclimatoceeas ulrichi White, Eocene, at 

 diameter of 140 MM. (X 7/10). 6, Suture of Nautilus pompilius Linnaeus, Recent, 



AT DIAMETER OF 140 MM. (X7/9). C, SUTURE OF EUTREPHOCERAS SLOANI ReESIDE, 



Eocene, at diameter of 120 mm. (X7/9). d. Suture of Eutrephoceras dbkayi 

 (Morton) of Meek, Cretaceous, at diameter of 100 mm., natural size. 



150 mm. in maximum diameter) ; stout, well rounded in all the stages 

 visible. Cross section of whorl moderately compressed, nephritic, 

 changing very little with increase in size of shell ; height and breadth 

 of the cross section about equal. Siphuncle dorsad of the center of 

 the septum. Umbilicus closed. 



Surface of shell not seen. Cast of interior smooth in both early 

 and late stages. 



Sutures are those of the genus — nearly straight with shallow ven- 

 tral lobe, ventrolateral saddle, lateral lobe and saddle, and umbilical 

 lobe. 



H olotype. —C'dt. No. 352,559 U.S.N.M. 



