496 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Nautilus Dt'kayi, Morton. 

 Plate 27, figs. 1, a, h, c, <?, e. 



Nautilus Dekayi, Morton (1834), Synop. Org. Remains, 33, pi. 8, fig. 4— Hall and Meek (1856), Memoirs 

 Am. Acad. Arts and Sci. Boston, V (n. s.), 406.— Meek and Hayden (1856), Proceed. 

 Acad. Nat. Sci. Philad., VIII, 280.— Conrad (1860), Jour. Acad. Nat. Sci. Philad., IV 

 (n. s.), 276 (not V. Dekayi as figured by Ernest Favre in Moll. Foss. Craie Env. de 

 Lemberg, pi. iii.fig. 1 to 3). 



? Nautilus perlatus, Morton (1834), Synop., pi. 13, fig. 4. 



Fig- 67. Shell subglobose, broadly rounded on 



the periphery and sides ; umbilicus closed ; 

 volutions increasing rapidly in size, or more 

 than doubling their diameter each turn, 

 about half as wide again as high, all hidden 

 but the last or outer one ; aperture much 

 wider than long, transversely reniform, the 

 lateral extremities being rounded, and the 

 Nautilus Dekayi. inner side deeply sinuous for the reception 



An outline from Morton's type-specimen, '.. ., ,. , . . , ,i 



showing the position of the siphon and the of the inner whorls; lip having a wide shal- 



form of the aperture, as indicated by one ] QW ginus n \ oy] g the peripheral side, promi- 

 of the inner septa. 



nently rounded on the lateral margins, and 

 again sinuous near each umbilicus; septa moderately concave, and about 

 sixteen or eighteen to each turn ; siphuncle small, located one-fourth to one- 

 third of the distance across toward the periphery, from the margin of the 

 inner side ; surface of adult or medium-sized specimens nearly smooth, or 

 having very obscure lines of growth, crossed by faint traces of longitudinal 

 striee; on young individuals, or the inner volutions of larger ones, these lines 

 are quite distinct in both directions, and form a very neat, cancellated style 

 of ornamentation ; internal casts sometimes showing a slender longitudinal 

 line on the center of the periphery. 



The proportions are shown by the following measurements of a young 

 individual: length, 1.84 inches; breadth of aperture, 1.70 inches ; diameter of 

 aperture in the direction of the length or greater diameter of the shell, 0.72 

 inch. Some imperfect adult individuals before me, too much broken to afford 

 exact measurements, were evidently as much as three times the linear dimen- 

 sions of that from which the foregoing measurements were taken. 



This common species has been wrongly identified with several foreign 

 forms. D'Orbigny, in his Prodr. de Paleont, expresses the opinion that his 



