14 OCTOPODID^. 



by cartilaginous styles), through the cartilaginous-shelled Cir- 

 roteuthis, to the decapods with horny pens : — then those with 

 calcareous plates and minute initial chambers, the latter of which 

 graduall}'- become larger, are siphunculated, curve, become spiral 

 and thus form a passage into the fossil tetrabranchiates and the 

 externally-shelled Nautilus. It is not impossible that in some 

 of the ancient genera, the structure of the animals was such as 

 to bridge over the gulf which now exists between the two orders: 

 this has been recently maintained by M. Munier-Chalmas, and 

 more cautiously by Dr. Paul Fischer. 



Suborder I. OGTOPODA. 

 Animal bursiform, bod}'' rounded or ovoid ; eyes fixed ; shell 

 usually absent, sometimes represented by internal cartilaginous 

 stylets, or externally by a calcareous nest for the eggs, formed 

 by the female only ; siphon without valve ; eight arms with fleshy 

 suckers (without corneous rings) on their inner face. Males 

 modifying one of their arms for copulation, and frequently 

 detaching it during the act. 



Family OCTOPODID^. 



Synopsis of Genera. 



a. Arms loith two rows of suckers. 



* Body not finned. 



Octopus. Bodyroanded. Arms long. Suckers sessile. Third 



right arm of male hectocot}- lized. 

 CiSTOPUS. Differs from Octopus in having a small aquiferous 

 sj'^stem, consisting of a bag with a small pore at its lower edge, 

 upon the web between each arm. 

 So^URGUS. Body oval, wider than the head ; arms short ; cups 



with narrowed bases. Third left arm hectocotylized. 

 Alloposus. Arms united by a web nearlj^ to the ends. 



* * Body finned. 



PiNNOOTOPUS. 



6. Arms with a single row of suckers. 

 * Not finned. 

 Eledone. Body rounded, without fins. Third right arm hecto- 

 cotylized. 

 BoLiT^NA. More gelatinous than Eledone ; suckers smaller, 

 less developed. 



* * Finned. 

 CiRROTEUTHis. Body with two transverse medial fins ; mantle 

 united to the head nearly all round, by a cervical band ; arms 

 united by a web nearly to their tips. 



c. Arms with three rows of suckers. 

 Tritaxeopus. • 



