16 AMERICAN MARINE CONCHOLOGY. 
Orver Il. PULMONIFERA. 
Lung breathers. Land and fresh-water snails. 
OrvER III. OPISTHOBRANCHIATA. 
Shell rudimentary or wanting. Branchiz arborescent, not pro- 
tected, but more of 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. 
OrverR 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. 
OrpER I. PROSOBRANCHIATA. 
Section A. SrpHONOSTOMATA. 
Carnivorous Gasteropoda. Shell spiral, axis usually imper- 
forate ; aperture notched or produced into a canal infront. Oper- 
culum horny, lamellar. 
* Lip of aperture expanded. 
Family Strompipz. Shell with an expanded lip, deeply notched 
near the canal. Operculum claw-shaped, serrated on the outer 
edge. 
** Lip of aperture not expanded. 
Family Muricipa&. Shell with a straight anterior canal; aper- 
ture entire behind. 
Family Buccornrp&. Shell simply notched in front ; or witha 
short canal abruptly reflected, producing a kind of varix on the 
front of the shell. 
Family Conrp@. Shell inversely conical or subfusiform ; aper- 
ture long and narrow; outer lip notched at or near the suture. 
Columella without plaits. 
Family Voturipa. Shell porcellanous, turreted or convolute ; 
aperture notched in front ; columella obliquely plaited. 
Family Cypraimpa. Shell porcellanous, convolute; spire con- 
cealed ; aperture as long as the shell, narrow, channelled at each 
end; outer lip of adult thickened, inflected. 
