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 Mollusca, 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. — Decapoda, Leach, 1S17. 



Naked Cephalopods, with an ovoid, cylindrical, or elongated body, having eight 

 symmetrical arms provided with pedunculated suckers, surrounded with horny rings, and 

 two long tentacular arras, proceeding from near the third and fourth 

 pair of arms, and expanded at their extremity, as in Sepia ele^ans, 

 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 SpiRULiOiE, (fig. 23) ; 

 and a phragmacone divided by numerous concave septa fitted upon a 

 style or pen, in the extinct BfiLEMNiTiDiE ; and in other fossil genera it p,^ 17 



varies from these types. ^'^^^ ^'^sans, d'Orbig. 



1. Family IjOiAGOVSiiDM, G^ray, 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 difi'ers in 

 the unequal length of the arms, which are six times as long as the animal itself. The 

 subjoined (fig. 18) CJiiroteutliis Feranyi, YerasssiC, 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.1;, d' Orbiyny, 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 laminse, with intervening spaces 



