180 
NAUTILIODEA. 
bilicus closed, or more or less widely open, as in JVautilus Barton- 
ensis of the Inferior Oolite and JS'. umbilicatas of the existing 
seas ; volutions deeply embracing and in section rounded, oval, or 
more rarely angular, as in N. triangularis of the Upper Greensand, 
or even channelled on the periphery, as in N. hexagonus of the 
Oxfordian. Siphuncle variable in position, from central to sub- 
central. Sutures more or less undulating, sometimes forming 
tongue-like lobes on the sides (subgenera Hercoglossa, Clydonautilus). 
An internal (dorsal) lobe (“ annular lobe ” of Hyatt) is present in 
many species, but it has a tendency to become obsolete in the 
adult shell, and is of no classificatory importance h Surface of 
the test either smooth, or ornamented with longitudinal ridges, 
or with transverse costas of varying strength ; the latter some- 
times divaricating upon the sides and periphery, as in N. plicatus. 
Type, Nautilus pompilius, Liune 
Trias to Recent ^ 
Subgenus HERCOGLOSSA, Conrad‘S, emend. Meek^. 
(^Grypoceras, Enclimatoceras, Hyatt®, Aganides, Zittel " {non Montfort).) 
Gen. Char. “ Shell more or less discoid, with umbilicus closed or 
small, and periphery usually rather narrowly rounded*^; volutions 
deeply embracing : surface nearly smooth, or with lines of growth ; 
septa deflected backwards in crossing each side, so as to form a deep, 
usually angular, lateral lobe ” {Meelc). Type, Nautilus orhiculatus, 
Tuomey 
Trias to Eocene. 
^ It was upon this feature that Montfort founded his genus Bisiphytes . — 
Conch. Syst. 1808, p. 55. 
^ Systema Naturae (ed. x.), p. 708. 
^ For remarks on Nautilus, see the Introduction to this volume. 
^ American Journ. of Oonchology, 1866, vol. ii. no. 2, p. 101. 
° United States Geol. Surv. Terr. 1876, vol. ix. p. 491. 
® Proc. Boston Soe. Nat. Hist. 1883, vol. xxii. pp. 269, 270. 
Handbuch der Palaeontologie, 1884, Band i. Abth. ii. Lief. iii. p. 383. 
® Sometimes flattened, as, in Naiitilus (Hercoglossa) franconicus, Oppel, or 
even sulcated, as in N. {H.) Picteti, Oppel. For other species of Hercoglossa 
see “Hie Cephalopoden der Stramberger Schichten,” in Oppel and Zittel’s 
‘ Palaeontologisehe Mittheilungen,’ 1868, Band i. Abth. ii. Atlas, pis. ii., iii., iv. 
On referring to the ‘Catalogue of Scientific Works’ published by B. Koch, 
Stuttgart (1880-1886), we find that this part of the Palaeont. Mitth. is erro- 
neously marked, both on the cover and titlepage, “ Zweiter Band, Erste Abthei- 
lung,” whereas it should be “ Erster Band, Zweite Abtheilung.” 
® Proceed. Acad. Nat. Sci. Philadelphia, 1854, p. 167. 
