MARINE MOLLUSCA OF THE UNITED STATES. 57 
nacreous inside; operculum calcareous and pauci-spiral, or horny 
and multispiral. ; 
III. Shell ear or limpet shaped, scarcely spiral; aperture basal, very large. 
Family X. JANTHINID#. Shell spiral, turbiniform; fragile; 
aperture large; outer lip notched in the middle; no operculum. 
Family XI. FissurELLIp#. Shell conical, limpet-shaped; apex 
recurved; nucleus spiral, often disappearing in the course of 
growth; anterior margin notched or apex perforated; muscular 
impression horse-shoe shaped, open in front. 
Family XII. Catyprraipm. Shell limpet-like, with the apex 
more or less spiral; interior simple or divided by a shelly process, 
variously shaped, to which the adductor muscles are attached. 
Family XIII. Parenti. Shell conical, limpet-shaped, the 
apex entire and turned forwards; muscular impression horse-shoe 
shaped, open in front. 
Family XV. Curronip&. Shell oval, composed of eight transverse 
imbricating plates, lodged in a coriaceous mantle, which forms 
an expanded margin round the body. 
IV. Shell tubular, symmetrical, open at both ends ; not spiral. 
Family XIV. Dentatiapa. (The tooth shells.) 
Family I. NATICIDA. 
The Natices, although possessing shells with entire apertures, 
are carnivorous animals, feeding principally on small bivalves, 
boring small round holes through their shells and rasping out the 
meat. 
Synopsis of Genera. 
Shell sub-globose ; spire rather elevated; aperture semilunar; columella 
adherent to and spirally produced into the umbilicus ; apex more or less 
dilated and truncate ; more rarely convex or rounded ; operculum horny, 
with a calcareous outer layer. Natica, Adanson. 
Shell oval, subglobose ; spire rather elevated ; aperture semilunar ; inner 
lip thin or with a moderate callus; umbilicus wide, pervious, not funicu- 
late. Operculum simple, cartilaginous. LunatiA, Gray. 
Shell orbicular, depressed ; spire flattened ; aperture wide, semilunar ; inner 
lip straight, callous; columella adherent to and spirally contorted into 
the umbilicus ; apex more or less dilated and truncate. Operculum simple, 
cartilaginous. NEVERITA, Risso. 
Shell ovate or suboyate, solid, smooth, usually without epidermis; spire 
small, acute, whorls simple ; aperture semicircular; inner lip oblique, 
thickened, callous; umbilicus funiculate; aperture adherent to and 
