THE CEPHALOPODA. 
171 
According to Madame Power and M. Rang, the Argonaut sits in its boat with its siphon 
towards the keel, as in figs. 15 and 16, swimming by the aid of its funnel action only, 
its dorsal arms being closely applied to the sides of the shell. It swims backwards 
by ejecting water from its funnel, and crawls at the bed of the sea in a reversed position, 
carrying its shell over its back. The Argonaut, like other testaceous MoUusca, secretes 
and forms the shell which it inhabits, although it does not adhere at any point to the 
shell, an observation long ago made and recorded by Aristotle. 
Section b. — Decapod a. Leach, 1817. 
Fig. 17. 
Sepia elegans, d'Orbig. 
Naked Cephalopods, with an ovoid, cyhndrical, or elongated body, having eight 
symmetrical arms provided with pedunculated suckers, surrounded with horny rings, and 
two long tentacular arms, proceeding from near the third and fourth 
pair of arms, and expanded at their extremity, as in Sepia elegans, 
d'Orb. (fig. 17). The body has a pair of lateral fins, and the funnel is 
usually provided with an internal valve. The eyes are large, movable 
in their orbits, and without lids. The nidamental gland is largely 
developed. The shell is calcareous and internal, and loosely lodged 
in the dorsal portion of the mantle in the Sepias. The style is formed 
of a cartilaginous blade or horny pen in the Calamaries. It is an 
internal siphoniferous polythalamous shell in the SpiRULiDiE, (fig. 23) ; 
and a phragmacone divided by numerous concave septa fitted upon a 
style or pen, in the extinct Belemnitid^e ; and in other fossil genera it 
varies from these types. 
1. i'^am/y LoLiGOPSiD^, 6^r ay, 1840. — Body elongated and tapering posteriorly ; fins 
large, broad, and mostly terminal. Shell an internal pen or gladius of horny structure, and 
consisting of a shaft and two lateral expansions. The Calamaries swim well, and crawl 
head downwards on their oval disc. 
2. Family Chiroteuthid^, Gray, 1849.— Body resembles preceding, but diff'ers in 
the unequal length of the arms, which are six times as long as the animal itself. The 
subjoined (fig. 18) Chiroteuthis Feranyi, Yevussac, shows the external development of the 
acetabular and tentacular arms. The gladius is elongated, enlarged at each end and 
tapers in the middle. 
3. Family Sepiad^, d'Ordiyny, 1835. — Body oval, fins lateral, as long as the mantle. 
Head large, united to the body by a broad nuchal band. Tentacular arms long, wholly 
retractile. Sessile arms having four rows of acetabula, with horny circles. Funnel with 
an internal valve. Shell long and wide, thick in front, concave internally behind, and 
terminating in a prominent mucro, composed of calcareous laminae, with intervening spaces 
