MARINE MOLLUSCA OF THE UNITED STATES. 



CLASS CEPHALOPODA. 



HEAD 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. 



ORDER OCTOPODA. 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. 



ORDER DECAPODA. 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. 



ORDER OCTOPODA. 



Family OCTOPODID^E. 



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 by a web. The animal is chiefly 

 littoral, inhabiting the temperate and tropical zones. It escapes 



