NAUTILI!)^. 
105 
Genus CCELONAUTILUS Poord. 
{Vestinmitilus, Eyckliolt^; Trematodiscus, Meek and 'VVortlien ^ ; 
Nautili Sulciferi, Nautili Cariniferi (pars), de Koninck ^ ; Phloioceras, 
Hyatt ’ j Trematoceras, Hyatt ®.) 
Gen. Char. Shell thick, discoid, with wide, very deep umbilicus, 
exposing all the volutions ; a central perforation is always present, 
and is very large in some species, as, for example, C. Meyerianus, 
de Kon. Volutions much wider than high, increasing rather rapidly, 
very slightly embracing, provided with more or less numerous angles 
or carinae. Periphery convex, very broad, sometimes having, es- 
pecially in adult specimens, a wide, shallow depression in the 
median line. Sutures nearly straight, except in passing over the 
periphery, where they make a more or less deep sinus. A dorsal 
(internal) lobe is present. 
Type, Nautilus styyialis, de Koninck". 
Carboniferous to Trias. 
' This name, from ko7\o}>, hollow (referring to the umbilicus), and Nautilus, 
is substituted for Trematodiscus, Meek and Wortlien, which was used by 
ITiickel for a genus of Eadiolarians. The name Trematoceras, proposed by 
Hyatt in lieu of Trematodiscus, is equally ineligible, because preoccupied, for 
although the species described by Eichwald (Leth. Ross. 18G0, vol. i. p. 1259) 
— Trematoceras disivrs — is a Bactrites, a generic name once used cannot be 
again employed, even for a different genus, without risk of confusion. The 
recommendations of the British Association on this point are explicit, as 
follows: — “ Classes of objectionable names” — q. “Some authors consider that 
when a name has been reduced to a synonym by the operation of tlie laws of 
priority, they are at liberty to apply it at pleasure to any new group which 
may be in want of a name. We consider, however, that when a word has once 
been proposed in a given sense, and has afterwards sunk into a synonym, it is 
far better to lay it aside for ever than to run the risk of making confusion by 
re-issuing it with a new meaning attached.” (From the British Association 
‘ Rules of Zoological Nomenclature,’ revised at the Birmingham Meeting, 
September 18G5 (pub. 18GG), p. 40.) 
^ Notice sur les Genres Nautilus, Vestinautilus, Asymptoceras, ka. (pamphlet, 
1852), p. 4. Also Hyatt, Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 294. 
^ Proc. Acad. Nat. Sci. Philadelphia, 18G1, p. 147. Geol. Surv. of Illinois, 
Palteont. vol. ii. 18GG, p. IGl. Report of the United States Geol Surv. of the 
Territories, 187G, vol. ix. p. 491. 
^ Faune du Calcaire Carbonifere de la Belgique (Annales du Mus. Roy. 
d’Hist. Nat. de Belgique, tom. ii.), pt. i. p. 90. 
® Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 286. 
® Ibid. p. 291 (footnote). 
~ Descrip, des Anim. Foss, du Terr. Oarbonif. de Belgique, p. 547, pi. xlv. 
flf. 11, a, h. 
