134 
NATJTTLOIDEA. 
The Nautilus Tmmilis of de Koninck’ bears some resemblance to 
the x^resent species, in its elevated periphery, the keeled margin of 
the umbilicus, and somewhat distant septa, but the whorls do not 
overlap so much as in C. infunclihuhim . N. humilis appears to be 
an immature shell. 
Horizon. Carboniferous Limestone. 
Locality. BoUand, Yorkshire. 
Represented in the Collection by two examples ; the one from 
Bolland (registered No. C. 228) is contained in the Gilbertson 
Collection.” 
Genus PLEURONAUTILUS% Mojsisovics^ 
(Group of Nautilus Trautscholdi, "Waageu b) 
Gen. Char. Shell thick, discoid, with a wide and moderately deep 
umbilicus, exposing all the volutions, and having a rather large 
central perforation. The whorls are subquadrate in section and 
very slightly embracing. The ornaments consist of strong, straight, 
or slightly bent transverse cos tee, nodose at the edge of the perijDhery 
and of the umbilicus, and sometimes also upon the sides. The 
periphery is smooth in some species (Pl euronautilus trinodosus, 
Mojs.^, P. ampezzanus., Loretz®, &c.), but in others the ribs overlap 
its edges and meet two ridges which form the boundary of a more 
or less shallow median furrow (Pleuronautilus Marmolatce, Mois."^, 
Nautilus transitorius, Waageu®, &c.). The sejita are simple, the 
sutures forming a shallow sinus upon the sides and periphery, and 
arching forward upon the lateral angles. The ventral sutures in 
full-grown individuals are nearly straight according to Mojsisovics. 
A small internal lobe is present. The siphuucle is a little below 
the centre. 
Devonian to Trias. 
^ Faune du Caleaire Carbonifere de la Belgique (Annalee du Mus. Roy. 
d’Hist. Nat. de Belgique, torn, ii.), p. 103, jil. xxiii. flf. 5a, bh. 
2 I h.ave slightly emended the diagnosis of this genus so as to include in it 
the Carboniferous forms. 
^ Die Cephalopoden der Mediterranen Triasx>rovinz (Abhandl. der k.-k. 
geol. Reichsanst. Band x.), 1882, p. 273. 
^ Mem. Geol. Surv. India — Palaeont. Indica, ser. xiii. Salt-Range Fossils, 1879, 
vol. i. p. 46 
^ Die Cephalopoden der Mediterranen Triasprovinz, 1882, p. 274. 
6 Ibid. p. 277. ' Ibid. p. 276. 
® Mem. Geol. Surv. India — Palieont. Indica, ser. xiii. Salt-Range Fossils, 
1879, vol. i. p. 53. 
