108 GENERA OF SHELLS. 



Sect. III.— NAKED CEPHALOPODA. 



The animals of this section have no shell either internal or 

 external, but the greater number of them contain a solid, 

 free, cretaceous or horny substance in the interior of their 

 body. 



SEPIARTA. 

 The sepiaria are marine animals, none of them have 

 any true shell ; they always live in the sea, some crawl- 

 ing at the bottom, as the octopus ; others, as the sepia 

 and loligo, swimming freely in the water, by means of 

 membranes or fins with which their sac is furnished. 

 This family contains four genera, 



Octopus, Loligopsis, Loligo, Sepia. 



Order V. — HETEROPODA. 



The body is gelatinous and transparent and the shell 

 of some of them resembles that of the argonauta. 



Carinaria. Shell univalve, conical, com- 

 pressed at the sides, unilocular, very thin, 

 hyaline ; apex spiral ; back sometimes with a 

 dentated carina. Aperture oblong, entire. 



C. vitrea, fragiUs, cymbium. 



Pterotrachea and Phylliroe, have no 

 shell. 



