The shells of this genus are fluviatile, and distinguished from the Melania by having the upper part of the columella callous. Shell oval or slightly sub-turriculated; aperture oval, without trace of tube, but hollowed anteriorly, without a posterior sinus; the columellar edge callous and rather deeply excavated; operculum horny, sub-spiral, rather complete. Melanopsis Buccinoides. M. costata. M. lævigata. _M. Buccinoides._ The Buccinum-shaped Melanopsis. Pl. 20, fig. 6. Species turriculated; colour bluish white, clouded with purple; spiral whorls dentated. _M. costata._ The ribbed Melanopsis. Species sub-turriculated and ribbed. _M. lævigata._ The polished Melanopsis. Species ovate, smooth, chestnut colour. 3. Pirena. Four species. This shell resembles the Melania, but is easily distinguished by having a sinus at the base and another at the summit. Shell turreted, aperture oblong, closed by a horny operculum; right lip sharp, with a distinct sinus at the base and another at the summit; base of the columella inclined towards the right. Pirena terebralis. P. spinosa. P. aurita. P. granulosa. _P. terebralis._ The wimble Pirena. Subulate, longitudinally striated, covered with a dark-brown epidermis; aperture white, outer lip expanded. FAMILY X. PERISTOMIDES. Three genera. 1. Valvata. One species. This genus contains shells found in fresh water. Shell sub-discoid or conoid, umbilicated, spiral whorls rounded; summit papillose; aperture round, not modified by the last whorl; the edges completely united, sharp; operculum complete, horny, and orbicular. _V. piscinalis._ The Pond Valvata. Pl. 20, fig. 5. Small, globular, conoid, deeply umbilicated; summit obtuse; wrinkled longitudinally, covered with a yellowish epidermis. 2. Paludina. Seven species. Generally inhabits fresh water, though some have been found where it is quite saline. Shell conoid, covered with epidermis, spiral whorls rounded; rather longer than broad, edges united, always sharp; the commencement of the left edge immediately attached to the last whorl of the spire; operculum horny, complete, or marginal, not spiral, with concentral elements. Paludina vivipara. P. achatina. P. Bengalensis. P. unicolor. P. impura. P. muriatica. P. viridis. _P. vivipara._ The viviparous Paludina. Pl. 21, fig. 1. Thin, ovate, ventricose, wrinkled longitudinally; body with three brown bands: covered with a greenish epidermis; aperture almost round.