CtASSTPTCATTON. 101 



SYSTEMATIC. 



Class CEPHALOPODA. 



Head large, separate from the bod}^, furnished with complex 

 ; 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 branchije or gills. Eyes sessile. Mandibles 

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

 suckers. Body sometimes laterallj- or posteriorly finned. Shell 

 internal, or none. 



Order 2. Tetrabranchiata. — Breathing by two pair of bran- 

 chiif. Mandibles shellj^ 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 flesh}^ bands. 

 No cephalic aquiferous pores. Arms subulate, elongated, more 

 or less united \)y webs ; their suckers sessile. 

 (Pelagic.) 



Family 2. Tremoctopid^ (Fhilonexid^). Front of mantle 

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

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

 on the back of the head. Suckers pedunculated. 



Family 3. Argonautid.^. Mantle supported by two buttons 

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

 or doi'sal 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. 



