9 
TAB. I. 
NAUTILUS Imperialism 
Gen. Char. Shell univalve; divided into chambers 
by numerous transverse septan connected by 
a siphunculus or tube. 
Spec. Char. Involute, umbilicate; aperture lunate ; 
septan entire, concave., broadest in the middle, 
truncated and slightly recurved at their ends ; 
siphunculus nearest to the inside. 
The axis of this species measures about two thirds of its 
greater diameter, and the septse are about one eighth of 
their width distant from each other : the umbilicus is pro* 
bably Open, in which it differs from Nautilus Pompiliuss 
the external coat is striated in the younger Shells and often 
of a light brown colour, under this the Shell is beautifully 
pearly ; the inside also is pearly. 
The upper figure shows a specimen from the great Clay 
stratum lately laid open at Highgate, and has some of the 
brownish outer coat remaining. It is broken at the mouth, 
which is closed by a pearly concave septa showing the 
aperture of the siphunculus, the other parts of the remains 
of the Shell are also pearly, and more or less iridescent. 
The broad undulations of the septae are seen in one part 
separated by shining brown Carbonate of Lime bearing a 
slight resemblance to a Lobster’s tail ; in another part the 
chambers are opened, the first of which is lined with the 
yellowish more waxy Carbonate of Lime and shows part of 
the siphunculus. The other septae are more or less broken, 
and show the chambers coated on the inside with brilliant 
variously coloured crystals of Pyrites, chiefly very small 
