16 AMERICAN MARINE CONCHOLOGY. 



Order II. PULMONIFERA. 



Luus 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. SipnoNOSTOMATA. 



Carnivorous Gasteropoda. Shell spiral, axis usually imper- 

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

 culum horny, lamellar. 



* Lip of aperture expanded. 



Famil}^ Strombid^. Shell with an expanded lip, deeply notched 

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

 edge. 



** Lip of aperture not expanded. 



Family MuRiciDiE. Shell with a straight anterior canal ; aper- 

 ture entire behind. 



Family Buccinid/E. Shell simply notched in front ; or M-ith a 

 short canal abruptly reflected, producing a ki)id of varix on the 

 front of the shell. 



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

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

 Columella without plaits. 



Family Yolutidjg. Shell porcellanous, turreted or convolute ; 

 aperture notched in front ; columella obliquely plaited. 



Family CYPR^EiDiE. Shell porcellanous, convolute ; spire con- 

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

 end; outer lip of adult thickened, inflected. 



