778 AUSTRALIAN OCTOPODILVE, 



Order 1. Bibranchiata. 



Sub-Order 1 . Octopoda. — Octopods, Argonauts, &c. 



Arms eight, sessile : no shell, but in lieu, with cartilaginous 

 styles encysted in the substance of the mantle : eyes fixed, 

 incapable of rotation. 



Sub-Order 2. Decapoda. — Cuttle-fish, Squids, &c. &c. 



Arms ten, of which eight are sessile and two, the longer ones, 

 tentacular : shell, gladius, or pen, internal, horny or calcareous, 

 so loosely suspended, as to fall out, when the bag which contained 

 it is opened : eyes moveable in their orbits : body elongated, 

 always with a pair of fins. 



Sub-Order 1. Octopoda. 

 Littoral. 



Family I. 'OCTOPODID^. 



Arms elongated, subulate, more or less united at the base by 

 a web : suckers sessile : no cephalic aquiferous pores : shell 

 represented by two short styles, encysted in the substance of the 

 mantle. 



Pelagic. 



Family II. TREMOCTOPIL^E, 



Suckers pedunculated : aquiferous pores on the back of the 

 head. 



Family III. ARGON AUTIDiE. 



The two upper or dorsal arms of the female only expand into 

 velamenta or broad webs at their extremity and secrete a sym- 

 metrical involuted shell : cups slightly pedicelled : two aquiferous 

 pores at the upper angle of the eye. 



Note. — The descriptions of Family IV. and subsequent ones 

 are for the present deferred, as they relate to the Decapods. 



