58 AMERICAN MARINE CONCHOLOGY. 



spirally contorted into the umbilicus, the apex more or less dilated, con- 

 vex, and rounded. Operculum large, horny, simple. MAMMA, Klein. 



Shell ventricose, imperforate ; spire with the apex acute ; whorls smooth, 

 without epidermis ; aperture very wide ; inner lip with a large smooth 

 callus covering part of the body-whorl and concealing the umbilicus. 



BULBUS, Bronn. 



Shell longitudinally oval, thin, smooth, white, not umbilicated, covered with 

 a light-brown epidermis ; spire elevated, suture canaliculated ; aperture 

 oval, produced in front. Operculum pauci-spiral, horny, thin. 



AMAUKOPSIS, Morch. 



Shell oval, flattened, ear-shaped, striated ; spire minute, depressed ; aper- 

 ture very wide, oblique ; umbilicus none ; inner lip curved posteriorly and 

 spread thinly over the body -whorl. Operculum very small and rudi- 

 mentary. SIGARETUS, Lamarck. 



Shell thin, small, ear-shaped, pellucid, fragile ; spire very small ; aperture 

 large, patulous ; inner lip receding. No operculum. 



MARSENINA, Gray. 



Shell thin, small, subglobose, composed of two rapidly enlarging volutions ; 

 aperture large, subovate ; lip thin, not joined behind ; usually covered 

 with a velvety epidermis. No operculum. VELUTINA, Blainville. 



Genus NATICA, Adanson. 

 Hist. Nat. Senegal, 172. 1757. 



1. N. AFFINIS, Gmelin. Fig. 94. 



(Nerita.) Syst. Nat., 3675. 1790. 

 N. dausa, Brod. et Sowb. Zool. Journ., iv. 360. 1829. 

 JV. consolidates, Couthouy, Bost. Journ. Nat. Hist., ii. 89, t.3, f. 14. 1838. 



Shell subglobose ; whorls four or five, subconvex, partially 

 flattened or even concave near the sutures ; spire very short, ob- 

 tuse ; suture distinct ; aperture oval, widest above ; lip sharp, 

 thickened, and rounded towards the umbilicus ; callus depressed, 

 enlarged at the upper angle, and in mature specimens quite con- 

 cealing the umbilicus ; epidermis thin, greenish-brown. Opercu- 

 lum and throat milk-white. 



Length 12.5, diameter 14 mill. 



Obtained from stomachs of fishes. 



Cape Cod, Mass., northwards (Eur.). 



2. N. PUSILLA, Say. Fig. 95. 



Jour. Philada. Acad. Nat. Sciences, ii. 257. 1822. 

 Shell thin, suboval, cinereous, or rufous, with sometimes one 

 or two obsolete, dilated, revolving bands ; columella callous ; 

 callus pressed laterally into the umbilicus, whitish ; umbilicus 



