Neritina perversa. N. pulligera. N. dubia. N. zebra. N. zigzag. N. gagates. N. lugubris. N. corona. N. brevispina. N. crepidularia. N. auriculata. N. Domingensis. N. fasciata. N. lineolata. N. semi-conica. N. strigilata. N. meleagris. N. Virginea. N. fluviatilis. N. viridis. N. Bætica. _N. fluviatilis._ The fresh-water Neritina. Shell very small, oval; back convex, smooth, white, with black or brown spots; spire inclined, lateral lip slightly denticulated; right edge sharp, operculum very oblique. _N. zebra._ The zebra or striped Neritina. Pl. 21, fig. 2. Same as N. fluviatilis, but striped instead of spotted. _N. corona._ The crown Neritina. Pl. 21, fig. 4. Species provided with long spines, and with the columellar edge denticulated. _N. auriculata._ The eared Neritina. Species with the columellar edge denticulated; the two extremities of the right edge extending beyond the aperture, and forming with the callosity, which is reflected over the columella, a kind or ear, produced by the tentacular lobe of the animal. _N. perversa._ The perverse Neritina. Species shaped like a Calyptræa, with the superior summit vertical, spiral; the last whorl forming all the base of the shell. 2. Navicella. Three species. A fresh-water shell, closely allied to the Neritina; it generally has the appearance of porcelain. Shell ovate oblong, covered with epidermis, shaped like a Patella, summit not spiral, but straight, turned quite to the base, and concave beneath; no columella; the columellar edge replaced by a kind of sharp partition, which covers part of the aperture, with a sinus at its left extremity; muscular impression shaped like a horseshoe, open in front and interrupted behind; thin, calcareous operculum, with a subulate, lateral tooth adhering to the posterior margin; the other edges sharp. Navicella elliptica. N. lineata. N. tessellata. _N. elliptica._ The oval Navicella. Shell covered with olive epidermis, under which it is smooth, shining, spotted and streaked with purple, blue, or brown; spire curved, prominent, extending beyond the margin. 3. Nerita. The Hoof Shell. Seventeen species. A marine shell, never spined, but variously striated. Some species of this genus are very beautiful; they are frequently worn as ornaments by the Indians.