CEPHALOPODA. 47 
A flat discoidal shell, rounded on the ventral aspect, and presenting obscure 
undulations similar to those which characterise JV. regalis. The aperture has 
an elongated, subquadrate shape; the umbilicus is narrow; the septa concave, 
and slightly undulated; they present on each side, in a line with the preceding 
whorl, a slight depression, which appears to be the first indication of the lateral 
lobes so fully developed in the WV. Parkinsoni; the siphuncle is excentric ap- 
proaching the dorsal margin; the dorsal lobes are short, very slightly concave, 
obliquely truncated, and not recurved. The lines of growth are prominent, and 
decussated more strongly than those of the two preceding species, and their undula- 
tions are broad and shallow. 
The Nautilus urbanus is distinguishable from JV. centralis by its flatness, and the 
greater length of its aperture; and from JV. regalis by its open umbilicus, the 
truncated extremities of the dorsal lobes of the septa, and its discoidal shape. It is 
a very rare shell. The figures 2a, 24, Tab, III, are taken from the shells drawn in 
‘Mineral Conchology, the only specimens with which I am acquainted. The larger 
one, belonging to Mr. Sowerby, was found in excavating St. Katharine’s Docks, 
near the Tower of London; the smaller one forms part of Mr. Bowerbank’s 
collection, and was obtained from Sheppy. 
The size of the larger individual figured is 7°4 in. in diameter, by 3°4 in. Fig. 4, 
Tab. VIII, represents the septum. 
No. 10. NAUTILUS IMPERIALIS. Sowerby. Tab. V. 
NAUTILUS IMPERIALIS. J. Sow. 1812. Min. Con. vol. i, p. 9, tab. 1, upper and right-hand 
figures. 
_ -- Defrance. 1825. Dict. des Sci. Nat., tome xxxiv, p. 297. 
— — Wether. 1836, Philos. Mag. and Journ. vol. ix, p. 465. 
—  Bucxuanpt. Michelotti. 1840. Indice ragionato, &e. p. 4. 
_ IMPERIALIS. Morris. 1843. Cat. Brit. Foss. p. 182. 
— _ Pictet. 1845. Traité élément. de Paléont. vol. ii, p. 338. 
_ _ Sowerby. 1849. Dixon’s Geol. Hist. &e. pp. 110, 120. 
N. Testé spheroidale ; umbilicatd, umbilicis angustis, profundis; apertura sub- 
ellipticd, semilunari ; septis undatis, siphone mediocri dorso-excentrali perforatis ; lobis 
dorsalibus latis et perparum reflexis. 
This species is easily distinguished from the JV. centralis by the excentric position 
of the siphuncle, as well as by the broad and reflected extremities of the dorsal lobes, 
which form, as it were, an axis to the shell. Its orbicular form, the lunate shape of 
the septa, and the recurved dorsal lobes, distinguish it as clearly from JV. rega/is and 
NV. urbanus. 
