50 
MELANIANA. —8 GeEneERa. 
Margins of the aperture of the shell disunited, the right always sharp. 
Mevan1A.—Shell turreted: aperture entire, oval or oblong, effuse at the base; columella 
smooth, incurved. Operculum horny. 
Plate XV. Fig. 13. M. amarula. (Helix amarula—Linn.) [Mrs. Mawe’s Cabinet. ] 
Metanopsis.—Shell turreted: aperture entire, oval-oblong.. Columella callous at the 
upper part; truncated at the base, separated from the right margin by a sinus. 
An operculum. 
Plate XV. Fig. 14. M. levigata. 
Pirena.—Shell turreted: aperture longitudinal, right lip sharp, having a sinus at the 
base, and another at the summit. Base of the columella curved towards the right 
margin: operculum horny. 
Plate XV. Fig. 15. P. terebralis. (Strombus ater.—Linn.) 
PERISTOMIANA.—3 Genera. 
Shell operculated, conoidal or subdiscoidal, the margins of the aperture united. 
VatvatTa.—Shell discoidal or conoidal, the whorls cylindrical, spiral cavity complete, not 
modified by the penultimate whorl; aperture round, the margins united, sharp. 
An orbicular operculum. 
Plate XV. Fig. 16. V. piscinalis. 
Patuptna.—Shell conoidal, the whorls rounded or convex, spiral cavity modified by the 
last whorl: aperture rounded-oval, oblong, angular at the summit; the two mar- 
gins united, acute, never reflected outwards. Operculum orbicular and horny. 
Plate XV. Fig. 17. P. vivipara. (Helix vivipara—Linn.) 
AmMPULLARIA.—Shell globular, ventricose, umbilicated at the base, without any callosity 
on the left lip: aperture entire, oblong, margins united, the right not reflected. 
An operculum. 
Plate XV. Fig 18. A. Guyanensis. 
NERITACEA.—4 Genera. 
Shell fluviatile, or marine, semi-globular or flattened-oval, without columella, the left margin of the 
aperture resembling a half partition. 
(1) FRESH-WATER SHELLS. 
NaviceLLa.—Shell elliptical or oblong, convex above, summit straight, depressed to the 
margin, concaye beneath; the left lip flattened, sharp, narrow, without teeth, 
transverse. A solid flat operculum, having an acute and lateral tooth. 
Plate XV. Fig. 19, 19 (a). N. elliptica. (Nerita porcellana.—Chem.) 
Neritmya.—Shell thin, semi-globular or oval, flattened beneath, not umbilicated: aper- 
ture semi-circular, the left margin flattened, sharp; no teeth or crenulations on the 
surface of the right margin. Operculum furnished with a lateral tooth. 
Plate XV. Fig. 20, 20 (a). N. dubia. (Nerita dubia.—Chem.) 
