XATJTILID^. 
131 
The species is verj’ globose, with a broadly rounded periphery, 
and a very deep umbilicus with steep sides, in which the whorls 
(about two and a half) are exposed. The edge of the umbilicus is 
keeled, and the whorls overlap to the margin of the keel, causing 
the dorsal side of the shell to be deeply emargiuate. There were, 
besides several fine spiral ridges on both sides of the keel, three or 
foul* on the inner, and one or two on the outer side ; these become 
obsolete in the adult shell, but they may always be seen upon the 
inner whorls. 
The section in this species is very broad in proportion to the 
height, the ratio of the ventro-dorsal to the transverse diameter 
being as 8 : 18, as measured in the most expanded part of a specimen 
consisting only of the septate part of the shell. 
The septa appear to be rather distant from each other, judging 
by de Koninck’s figure (loc. cit. pi. x. f. 2 b ) ; they are not seen in 
the British Museum specimens. The siphuncle is situated between 
the centre and the peripheral margin. The test appears to be 
quite smooth, nothing but faint lines of growth being seen (type 
specimen). 
Bemarl’S. This species may be readily distinguished by its very 
broad and globose whorls, deep umbilicus, and the keels surrounding 
the latter in the young shell. 
Horizon. Carboniferous Limestone. 
Locality. BoUand, Yorkshire. 
WeU represented in the Collection, which contains (“ Gilbertson 
Collection ”) the type specimen described by Phillips in the ‘ Geology 
of Yorkshire ’ (loc. cit.). 
Coelonautilus Derbiensis, Eoord. 
1878. Nautilus Chesterensis, de Koniuck, Faune du Calcaire Carboni- 
fere de la Belgique (Annales du Mus. Roy. d’Hist. Yat. de Bel- 
gique, tom. ii.), p. 97, pi. xxxi. If. 4, a-c (excL pi. xxiii. ff . 3, a-c). 
1888. Nautilus Chesterensis, Tzwetaev, Memoires du Comite Geolo- 
gique [St. Petersburg], vol. v. no. 3, p. o4, pi. v. if. 19-22. 
[Ab^ 1866. Nautilus Chesterensis, Meek and Worthen, Geol. Surv. of 
Illinois, vol. ii. Palaeont. p. 306, pl. xxiv. ff . 4 «, 4 &.] 
Char. Shell subglobose, composed of three whorls, of which 
the later ones cover the preceding ones to the extent of about one 
half, all, however, being exposed in a deep umbilicus. The peri- 
phery is broad and rounded at the sides ; the walls of the umbilicus 
are very steep. The body-chamber constitutes about one half of 
the last whorl, its outline is sigmoidal at the sides, and it is deeply 
