CEPHALOPODA. 



523 



Octopods, besides wanting the long tentacula, 

 are also characterized by the absence of man- 

 tle-fins, and consequently are limited to retro- 

 grade progression while swimming ; their ace- 

 tabula are sessile and unarmed ; they have two 

 oviducts, but without detached glands for secre- 

 ting a nidamentum. 

 Family TEST ACE A. 



Body oblong, rounded ; mantle adhering 

 posteriorly to the head ; first, or dorsal 

 pairs of arms dilated and membranous 

 at the extremity; (c, 1, fig. 206.) 

 Funnel without a valve, but articulated 

 at its base by two ball-and-socket joints 

 to the inner sides of the mantle. Bran- 

 chial hearts with fleshy appendages. 

 No internal horny or testaceous rudi- 

 ments ; but an external monothalamous, 

 symmetrical shell, containing, but not 

 attached to, the body of the animal; 

 which also deposits its eggs in the cavity 

 of the shell. 



Genus ARGONAUTA, Linnaeus. On the 

 supposition that the shell is parasitically 

 occupied by the Cephalopod, but formed 

 by some other mollusk, some natu- 

 ralists limit the above generic title to 

 the shell, and call the Cephalopod 

 Ocythoe.* We shall, however, con- 

 tinue to apply the term Argonauta to the 

 Cephalopod in question, as the evidence, 



Fig. 



though strong, is not conclusive of its 

 parasitic nature. The character of the 

 Family is also that of the Genus. 



Ex. Argonauta Argo, Linn. (fig. 200.) 



Genus Bekrophon, founded on the fossil 

 remains of a shell resembling in family 

 characters that of the Argonauta. 



Ex. Belerophon apertus, Sowerby. 

 Family NUDA. 



Body generally rounded, mantle broadly 

 continuous with the back of the head. 

 Arms connected at the base by a broad 

 web : first pair elongated, and gradually 

 narrowing to a point. Funnel without 

 an internal valve or external joints; 

 branchial hearts without fleshy appen- 

 dages ; biliary ducts without follicular 

 appendages. Shell represented by two 

 short rudimental styles, encysted in the 

 dorso-lateral parts of the mantle. 



Genus OCTOPUS, Leach. The arms pro- 

 vided with a double alternate series of 

 sessile acetabula. 



Ex. Octopus vulgar is, Cuv. the Poulp or 

 Preke, (fig. 210, in which this species 

 is represented in the act of creeping on 

 the shore ; its body being carried verti- 

 cally in the reverse position with the 

 head downwards ; its back being turned 

 to the spectator, towards whom it is 

 supposed to be advancing.) 



210. 



The Poulp, Octoptu vulgaris, Cuv. 



* Should the above suspicion be proved to be 

 well founded, we conceive that it would be more 

 appropriate to retain the term Argonauta, in order 



to designate the Cephalopod which navigates the 

 frail bark ; and revert to the original name of 

 Cymbium for the shell, which was applied to it by 



2 M 2 



