118 MANUAL OF NATURAL HISTORY. 



eight or ten fleshy arms ; a tube or siphuncle used 

 in locomotion ; sexes separate ; shell internal or 

 external. 



I. ORDER— Octopods (Octopoda). 



Body roundish ; head with eight fleshy arms fur- 

 nished with sessile cups or suckers ; eyes fixed ; gills 

 two ; shell none or rudimentary. 



1. Family. — Octopods (Octopodidse). Arms similar, 



elongated, united at the base by a web, mantle 

 supported by fleshy bands ; cephalic aqui- 

 ferous-apertures none ; shell represented by 

 two short styles in the substance of the 

 mantle. Littoral. 



2. Family. — Pelagian - Octopods (Philonexidse). 



Arms subulate ; cups peduncled, in two rows ; 

 eyes large and prominent ; mantle supported 

 by two buttons at base of siphuncle fitting 

 into grooves of mantle ; shell none. Pelagian. 



3. Family. — Argonauts (Argonautidee). Arms subu- 



late, the two upper dilated, secreting (in the 

 female) a symmetrical involute shell ; mantle 

 supported by two buttons fitting into grooves 

 at base of siphuncle; shell externa], one- 

 celled, thin ; apex involute. 



II. OEDEK — Decapods (Decapoda). 



Body naked, more or less elongated; head with 

 ten fleshy arms, the two longer or (tentacular) arms 

 with peduncled cups with horny rings ; eyes free in 

 orbit ; gills two ; shell internal, medial. 



