264 
XAUTILOTDEA. 
Nautilus arcuatus, Deshaycs \ 
1842. Nautilus arcuatus {arque), Leymerie, Suite du M^ni. sur le 
Terrain Cretace du Departement de I’Aiibe, pt. ii. ^ ; M^m. Soc. 
Geol. de France, vol. v. pt. i. p. 14, pi. xviii. ff. 1 a, 1 b. 
1846. Nautihis arcuatus, Leymerie, Statistique Geolo^que et ^lint^ra- 
logique du Departement de I’Aube, p. 16o. 
1852. Nautilus arcuatus, Giebel, Fauna der Vorwelt, Band iii. Abtb. i. 
p. 182. 
1859. Nautilus arcuatus, Pictet and Campiclie, Descrip, des Fossiles du 
Terrain Cretace des Environs de Sainte-Croix (Pal. Suisse), ser. ii. 
pt. i. p. 140. 
1877. Nautilus arcuatus, Jukes-Browne, Supplementary Notes on the 
Fauna of the Cambridge Greensand, Quart. Journ. Geol. Soc. 
vol. xxxiii. p. 488. 
1881. Nautilus arcuatus, Jukes-Browne, in Penning and Jukes-Browne, 
Geology of the Neighbourhood of Cambridge, Mem. Geol. Surv. 
England and Wales, Appendix B, p. 151. 
Sp. Char. Shell inflated in the middle, and having a subangular 
periphery, with scarcely any umbilicus ; septa as wide as high and 
very sinuous (tres arquees) ; siphuncle situated a little below the 
centre. Test thin, and marked only with a few annulations and 
striae of growth, distinct only in the young shell. 
Remarlcs. This species resembles Nautilus Fleuriausianus, d'Orb. ; 
hut the whorls of the latter are less embracing, the septa have not 
the same form, and the siphuncle is differently situated. The same 
differences separate the present species from N. Clementinus, d’Orb., 
which has besides a more rounded periphery. 
Referring to the present species, Mr. Jukes-Browne (loc. cit.) 
remarks : — “ Several casts agreeing in every respect with the figure 
and description of N. arcuatus have been found in the ‘ Nodule- 
bed,’ though they are by no means common. They are easily dis- 
tinguished from all others by the absence of any umbilicus, and by 
the pinched-up hack; this character is very conspicuous in the 
inner whorl, but becomes gradually less in the later chambers.” 
He adds : — ‘‘ The species was found by Leymerie in the Gault of the 
^ I may take this opportunity of observing that Giebel (Fauna der Vorwelt, 
Bd. iii. Abth. i. p. 182) credits Leymerie with the authorship of this species ; 
but the latter explains in the first part of his memoir that M. Deshayes de- 
termined a great part of the species already known, and separated from them 
the new species. The latter therefore have the name of Deshayes attached to 
them in M. Leymerie’s descriptions. 
- The first part of this memoir is contained in Mem. Soc. Geol. de France, 
1841, vol. iv. pt. ii. p. 291. 
