CLASSIFICATION. 



SYSTEMATIC. 



CLASS CEPHALOPODA. 



Head large, separate from the body, furnished with complex 

 eyes ; mouth with a pair of mandibles or beaks, resembling those 

 of a parrot, edged with fleshy lips, and surrounded by a circle 

 of arms. 



Order 1. DIBRANCHIATA. Breathing by a single pair of inter- 

 nal symmetrical branchiae or gills. Eyes sessile. Mandibles 

 horny. Arms, eight or ten, furnished with rows of acetabulse or 

 suckers. Body sometimes laterally or posteriorly finned. Shell 

 internal, or none. 



Order 2. TETRABRANCHIATA. Breathing by two pair of bran- 

 chiae. Mandibles shelly. Arms very numerous, without suck- 

 ers. Shell external, chambered ; capable of containing the 

 animal. 



ORDER I. DIBRANCHIATA. 



Sub-Order 1. OCTOPODA. Arms eight, sessile ; no shell.* 

 Sub-Order 2. DECAPODA. Ten arms, of which eight are sessile, 

 and two (longer) tentacular. Shell internal. 



SUB-ORDER I. OCTOPODA. 



(Littoral.} 



Family 1. OCTOPODID^. Mantle supported by fleshy bands. 

 No cephalic aquiferous pores. Arms subulate, elongated, more 

 or less united by webs ; their suckers sessile. 



(Pelagic.} 



Family 2. TREMOCTOPID^: (PHILONEXID^E). Front of mantle 

 supported by two buttons at the base of the siplmncle, fitting 

 into grooves on the inner side of the mantle. Aquiferous pores 

 on the back of the head. Suckers pedunculated. 



Family 3. ARGONAUTID^E. Mantle supported by two buttons 

 fitting into grooves at the base of the siphuncle. The two upper 

 or dorsal arms (in the female only) expanding into velamenta 

 or broad webs at their extremity, from which an egg-nest (shell) 



*The so-called external shell of the argonaut, is the egg-nest of the 

 female. 



