INVERTEBRATE PALAEONTOLOGY. 499 



Nautilus elegans, Sowerby. 



Plate 8, figs, 2, «, b, c. 



Xaulilua elegans, Sowerby (181G), Min. Conch., II, 3:5, pi. 11(5.— Mautell (1822), Geol. Sussex, 112, tab. xx, 



fig. 1.— Sharpe (1853), Mouogr. Cbalk Ceph. of England (Paloeoutogr. Soc), 12, pi. 



iii, fig. 3 ; and pi. iv, fig. 1 (probably not of d'Orbigny, Paleout. Fr., Terr. Cr€t., 1,87, 



pi. 19, and some ot hers). 

 Nautilus elegans, var. Nebrascensis, Meek and Hayden (1862), Proceed. A'-ad. Nat. Sci. Pbilad.,XIV, 25. — 



Meek (1864), Smithsonian Check-List N. Am. Cret. Fossils, 25. 



Shell subglobose, broadly rounded over the periphery, and on each side 

 to the umbilicus, which is closed in young and medium-sized specimens, 

 but becomes a little open in the adult ; volutions increasing rapidly in size 

 considerably wider transversely than in the dorso-ventral direction, all of those 

 within entirely embraced and hidden by the last one; aperture transversely 

 reniform-sublunate, being profoundly sinuous on the inner side for the recep- 

 tion of the inner turns ; margins of the septa arching forward a little near 

 the umbilicus, slightly waved backward on the sides, then again curving very 

 slightly forward as they approach the periphery, in crossing which they bend 

 again almost imperceptibly backward ; siphuncle placed a little outside of 

 the middle of the septa; surface of the outer volution ornamented by regular 

 flattened, transverse costse (about five times as broad as the narrow, shallow 

 grooves between), and moderately distinct lines of growth, which, like the 

 costae, in crossing over the periphery, arch gracefully and deeply backward, 

 parallel to the deep peripheral sinus of the margin of the lip. 



Length, or greatest diameter, about 3.90 inches; height, 2.82 inches ; 

 breadth at aperture, 3.40 inches. 



In originally publishing a notice of this shell, in the Proceedings of the 

 Academy, as a variety of N. elegans, Sowerby, we remarked that it agrees 

 almost exactly in form and surface-markings with Sharpe's figures of N. 

 elegans (Sowerby's figure being less satisfactory because it shows only an 

 oblique lateral view), but that it seemed to differ in having its umbilicus 

 closed at all ages, and its, siphuncle slightly more nearly central. At that 

 time, we were under the impression that a peculiar rounded projection shown 

 on the left side of figure 2, a, of plate 8, was a kind of columella formed by 

 the thickening of the lip, thus completely filling the umbilicus as in N. 

 Dekayi. 



A more critical examination, however, and the removal of some adher- 

 ing laminae of shell, have led to the conclusion that this round columella- 



