4 HOYLE, Genera of Recent Dibranchiate Cephalopoda. 



KEY. 



I'Suckers sessile, with no horny ring ; normally with 



eight arms (OCTOPODA) i2 



I Suckers stalked, with a horny ring ; normally with eight 



arms and two tentacles (DECAPODA) 20^ 



'A pair of oar-shaped fins projecting from the sides of 



the body ; suckers in a single row (Cirroteuthid^) 2 



iNo oar-shaped fins 5 



^Body not depressed, length at least equal to breadth ... 3 



, Body much depressed, not distinctly separated from the 

 ^ arms ; whole animal disc-shaped Opisthoteuthis. 



iA well- developed web between the arms 4 

 No web between the arms Fivekenia? 



^Internal cartilage saddle-shaped, placed transversely 



across the body Cirroteuthis. 



Internal cartilage horse-shoe shaped ; placed around 

 the aboral extremity of the body Stauroteuthis. 



'Mantle adherent to the funnel in the middle line 

 ventrallyj so that there are two openings into the 

 mantle cavity, one on either side. (Amphitretid^). 



AmphitretusJ^ 



Mantle aperture single. , 6 



An external shell. ( ARGONAUxiDiE) Argonauta ? . 



6. 



[No external shell 7 



{Body soft and gelatinous. (Alloposid^) 8 

 Body firm 9 



