77 
NAUTILUS. 
A. Spiral, rounded, with contiguous whorls. 
(Plate XII. Fig. 2.) 
B. Spiral, rounded, with separated whorls. 
(Fig. 3.) 
C. Elongated and straightish. 
Shell univalve, convolute, smooth, many-cham- 
bered, the divisions perforated and connected by a 
continued siphunculus or pipe, formed of a thin, 
testaceous matter, and lined with a membrane of 
the animal. The dissepiments are convex inwardly, 
and the chambers become gradually larger from 
the tip ; in the last or external one of which the 
animal is supposed to fix his habitation, keeping 
up a communication with his interior apartments 
by means of the hollow tube which passes through 
them all. 
This and the preceding genus have many natu- 
ral characteristics common to both ; but they are 
distinctly separated by the circumstance of one 
being concamerate, the other not so. The inhabit- 
