296 CLASS V. CEPHALOPODA. ORDER I. POLYTHALAMIA. 
Spirula even is founded upon the single testimony of Péron and Lesueur, 
and no other specimen than the one which they described having as yet 
been seen, it cannot but be considered to be involved in some uncertainty ; 
one French traveller, indeed, Fréminville, has challenged the authenticity 
of their description. 
The shell of Spirula may be described as being for the most part in- 
ternal, white, transparent and tubular, rolled into a discoid spire, with 
the whorls entirely separated from each other; it is then regularly divi- 
ded or partitioned by a number of transverse septa, which are convex on 
the inner side, and there is a continuous siphon running throughout from 
chamber to chamber, near the ventral part of the shell; the aperture has 
been always found entire, with the margins simple and acute, but we are 
not yet satisfied that this is the mature completion of the shell. 
Example. 
Pl. CCXCVIII. Fig. 1 to 3. 
Sprruta Peronu, Lamarck, Anim. sans vert., vol. vii. p. 601. Martini, 
Conch., vol. i. pl. 254. Vignette 11. f.1 to 3; De Blainville, Anato- 
mie de la Coquille de la Spirule, Nouvelles Annales du Muséum, 
vol. ili. p. 18. pl. 1. f. A. to F. 
Spirula australis, Encyclopédie Méthodique. 
Cornu Ammonis, D’Argenville, Martini. 
NAUTILUS, Aristotle. 
Testa orbicularis, symmetrica, anfractibus plurimis, in spiram discoi- 
deam contigué volutis, ultimo alios obtegente, spira utrinque um- 
bilicata, umbilico aut perspicuo, aut occulto ; multilocularis, loculis 
regularibus, septis transversis, interné convexis, siphunculo conti- 
nuo subcentricé perforatis. 
The two great conchiferous Cephalopods, Argonauta and Nautilus, 
