16 AMERICAN MARINE CONCHOLOGY. 



Order II. PULMONIFERA. 



Lung breathers. Laud and fresh-water snails. 



Order III. OPISTHOBRANCHIATA. 



Shell rudimentary or wanting. Branchiae arborescent, not pro- 

 tected, but more or less completely exposed, on the back or sides 

 of the body near the rear end. Sexes united. 



A few species, Bulla for example, have a shell enveloped in the 

 mantle. 



Order IV. PTEROPODA. 



Marine animals swimming by the aid of a pair of wing-like fins 

 proceeding from the sides of the mouth or neck. Shell glossy 

 and translucent. Sexes united. Pelagic. 



Order I. PROSOBRANCHIATA. 



Section A. Siphonostojiata. 



Carnivorous Gasteropoda. Shell spiral, axis usuall}' imper- 

 forate ; aperture notched or produced into a canal in front. Oper- 

 culum horny, lamellar. 



* Lip of aperture expanded. 



Family Strombid.e. Shell with an expanded lip, deepl} 7 notched 

 near the canal. Operculum claw-shaped, serrated on the outer 

 edge. 



** Lip of aperture not expanded. 



Family Muricid.e. Shell with a straight anterior canal ; aper- 

 ture entire behind. 



Family Buccinid.e. Shell simply notched in front ; or with a 

 short canal abruptly reflected, producing a kind of varix on the 

 front of the shell. 



Family Conid.e. Shell inversely conical or subfusiform ; aper- 

 ture long and narrow; outer lip notched at or near the suture. 

 Columella without plaits. 



Family Yoletid;e. Shell porcellanous, turreted or convolute ; 

 aperture notched in front ; columella obliquely plaited. 



Family CYPRiEiD^;. Shell porcellanous, convolute; spire con- 

 cealed ; aperture as long as the shell, narrow, channelled at each 

 end; outer lip of adult thickened, inflected. 



