2. Genus Pirena. Pl. [X].
Animal. Much elongated, mantle prolonged into a canal at the left side, but without distinct tube; foot short, oval, with an anterior marginal furrow; head terminated by a depressed proboscidiform muzzle; tentacula very distant, thickly annulated, dilated in the inferior half of their length, and having the eyes at the summit of this dilation; mouth a terminal and vertical slit, without labial tooth, and with a very small tongue; a single long and narrow branchia.
Shell. Distinguished from the preceding genus by having a sinus at the base, and another at the summit; turreted; aperture longitudinal, right lip sharp, base of the columella inclined to the right. Inhabits the rivers of India and Africa. One species is found in America. Six species.
- Pirena terebralis.
- P. cancellata.
- P. aurita.
- P. spinosa.
- P. granulosa.
- · · · · ·
- P. scalariformis.*
3. Genus Melanopsis. Pl. [X].
Animal. As preceding genus.
Shell. The Melanopsis is distinguished from the Melanaia, by the columella being callous in the upper part, and the base truncated as in the Achatina, and differs from the Pirena in having only a sinus or widened opening at the base of the shell; aperture covered by a horny operculum. Inhabits the rivers of the Archipelago. Three species.
- Melanopsis costata.
- M. lævigata.
- M. prærosa.