MARINE MOLLUSCA OF THE UNITED STATES. 
Ciass CEPHALOPODA. 
HeApD large, separate from the body; eyes large, complex, lateral: 
ears developed; mouth armed with two horny or shelly jaws edged 
with fleshy lips, surrounded by eight or ten fleshy arms and fur- 
nished with an entire or slit tube or siphuncle. Body ovate, round- 
ish or cylindrical, open in front, containing the viscera and one 
or two pairs of internal symmetrical gills; naked ; surrounded by 
a thin shell with a single cavity; or partly or entirely contained 
in the last chamber of a chambered shell furnished with a siphon 
passing from chamber to chamber. Unisexual. Animal free, 
walking head downwards by means of its arms, or swimming in 
the sea, propelled by the water from the siphon tube. 
OrpDER Ocropopa.—Body naked; head separate, with eight 
fleshy arms, furnished with sessile cups or suckers, without any 
horny rings; eyes fixed in the skin. Siphuncle entire; gills two. 
No internal or external shell. 
OrpER Drecapopa.—Body naked; head separate, with ten fleshy 
arms, two of them longer, furnished with pedunculated cups or 
suckers, with horny rings; eyes free in their orbits. Siphuncle 
entire; gills two. Having an internal shell or pen. 
OrpER OCTOPODA. 
Family OCTOPODID. 
Arms subulate. Mantle supported by fleshy bands. No cephalic 
aquiferous apertures. 
In the genera comprising this family the arms are similar, 
elongated, and united at the base bya web. The animal is chiefly 
littoral, inhabiting the temperate and tropical zones. It escapes 
