CEPITALOPODS. 471 
the branchiz or gills being four, in having no suckers, and in having 
an external shell. The number of living species is extremely small— 
for this group of animals belongs peculiarly to the earlier ages of our 
globe—is gradually becoming extinct, and presents in our days only 
some species very rare and few, especially when we compare them 
with the prodigious numbers of these beings which animated the seas 
of the ancient world. In fact, the only ving genus of the order is 
that of Mauti/us, the external shell of which has a singular resem- 
blance in form to the internal shell of the genus Argonauta. 
In Nautilus the shell has a regularly convoluted form, the last 
whorl being equal to all the others. It is divided internally into 
Fig. 320.- Nautilus pompilius (Linnzus), 
showing the interior of the lower cell, to which the animal is fixed. 
numerous cells, formed by transverse partitions, concave in front and 
perforated towards the centre, and forming a kind of funnel, which 
gives passage to a respiratory syphon. 
In the last partition of the shell (Fig. 320) is the animal, covered 
by its mantle, which lines the walls of the partitions. When it 
contracts itself it is protected by a sort of triangular and fleshy hood. 
Numerous tentacles, which are retractile, within sheaths, or “ digita- 
tions,” corresponding to the eight ordinary arms of a cuttle-fish, and 
some of them furnished with numerous lamellz, surround the head, 
which is, besides, scarcely distinguished from the body. The head 
bears two great projecting eyes, each planted upon a peduncle. 
Like Sepia and Octopus, the mouth of the JVauti/us is armed with 
mandibles, fashioned somewhat like the parrot’s beak. The branchiz, 
as we have seen, are four in number ; the circulatory system consists 
