96 MOLLUSCA. 
The nautilus spirula of Linnzeus has afforded characters 
for the construction of anew genus termed Srrruta. The 
whorls are separate, the mouth orbicular, the partitions per- 
forated by a tube, and the last turn of the spire prolonged 
in a straight line. This last character was unknown to Lin- 
naeus, who had only seen the spiral body of the shell. 
The genus Sprroxina has the last turn of the spire pro- 
duced like the preceding, but the whorls are contiguous, 
The partitions are perforated by a tube. 
The genus Lrrvota is allied to the spirula and spirolina 
in the production of the last whorl. The spires of the body 
are contiguous, and the partitions are pierced by a number 
of holes. 
In the preceding genera the inner walls of the cavity are 
simple ; but in the two following, the walls are formed into 
joints by sinuous sutures. The first of these is the AMMo- 
NITES, including those shells which have been termed cor- 
nua ammonis. The origin of this name is, by some, sought 
for in their resemblance to the horns of a ram; by others, 
to their having been found near the temple of Jupiter Am- 
mon in Upper Egypt. By the Indians, the ammonites 
sacer is considered as a metamorphosis of the god Vishnu, 
and termed by them salgram or salgraman. It is found 
among the peebles of the Gandica where it joins the Gan- 
ges. In this genus the whorls are contiguous, spiral, de- 
pressed, and obvious. 
The Orsuuites of Lamark differs from the ammonites 
in the circumstance of the last whorl embracing and con-_ 
cealing the others. In both the syphon is marginal. 
Nearly allied to the preceding is the Turrirres of 
Montfort. It is similar in internal structure, but while the 
shells of the former are spirally discoid, those of the present 
