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 
gradually 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. 
SuporDEeR I. OC TOPODA. 
Animal bursiform, body 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. 
Famity OCTOPODID 2. 
Synopsis of Genera. 
a. Arms with two rows of suckers. 
* Body not finned. 
Ocropus. Body rounded. Armslong. Suckers sessile. Third 
right arm of male hectocotylized. ; 
Cisropus. Differs from Octopus in having a small aquiferous 
system, consisting of a bag with a small pore at its lower edge, 
upon the web between each arm. 
Scaureus. Body oval, wider than the head; arms short; cups 
with narrowed bases. Third left arm hectocotylized. 
Aioposus. Arms united by a web nearly to the ends. 
* * Body finned. 
PINNOCTOPUS. 
b. Arms with a single row of suckers. 
* Not finned. ; 
Exieponté. Body rounded, without fins. Third right arm hecto- 
cotylized. 
Bonirana. More gelatinous than Eledone; suckers smaller, 
less developed. 
* * Finned. 
Crrrorgutuis. 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. 
