Fam. 28. Nerineidae.—Shell solid, long, sub-cylindrical, aperture channelled, columella and interior of whorls with continuous ridges, extending up the spire. Genera: Nerinea (Trias to Cretaceous), Aptyxiella (Jurassic).
Fam. 29. Melaniidae.—Border of mantle festooned, foot broad, with an anterior groove, penis present; radula closely resembling that of Cerithium; shell long, spiral, with a thick periostracum, surface with tubercles, ribs, or striae, suture shallow; operculum corneous, paucispiral, nucleus excentrical. Animal ovoviviparous. Fresh water. Cretaceous ——. Principal genera: Melania (with many sections or sub-genera), Pachychilus, Claviger (= Vibex), Hemisinus, Pirena, Melanopsis, Tiphobia, Paludomus (subg., Philopotamis, Tanalia, Stomatodon), Hantkenia (Eocene), Larina (?).
Fam. 30. Pleuroceridae.—Mantle edge not festooned, no copulatory organ, otherwise like Melaniidae; operculum with nucleus sub-marginal. Animal oviparous. Fresh-water. Cretaceous ——. Genera: Pleurocera (including Io, Fig. [12], p. 16, Angitrema, Lithasia, Strephobasis), Goniobasis, Anculotus, Gyrotoma.
Fam. 31. Pseudomelaniidae.—Shell resembling that of Melaniidae, but marine. Genera: Pseudomelania, Loxonema, Bourguetia, Macrochilus. Palaeozoic to Tertiary strata.
Fig. 275.—Melania confusa Dohrn, Ceylon.
Fam. 32. Turritellidae.—Mantle with a siphonal fold on the right side; radula variable (p. [224]); shell long, whorls many, slowly increasing in size, transversely ribbed or striated, aperture small; operculum corneous, nucleus central. Jurassic ——. Principal genera: Turritella, Mesalia, Protoma, Mathilda (?).
Fam. 33. Coecidae.—Tentacles long, eyes sessile at their base; shell small, spiral in the young form, spire generally lost in the adult, the shell becoming simply a straight or curved cylinder; operculum corneous, multispiral. Eocene ——. Single genus, Coecum.
Fam. 34. Vermetidae.—Visceral sac greatly produced, irregularly spiral, no copulatory organs (radula, Fig. [126], p. 223), shell tubular, irregularly coiled, last whorls often free, aperture circular; operculum corneous, circular, nucleus central. Carboniferous ——. Principal genera: Vermetus; Siliquaria (Fig 153, p. 248), a long fissure, or series of holes, runs along a considerable part of the shell, operculum with outer face spiral, elevated.
Fam. 35. Strombidae.—Foot narrow, arched, metapodium greatly produced, snout long, eye peduncles long, thick, eyes elaborate, siphon short, penis prominent, bifurcate; central tooth with strong median cusp, marginals falciform, slender, edge more or less denticulate; shell solid, spire conical, outer lip generally dilated into wings or digitations, channelled before and behind, a labial sinus at the base, distinct from the anterior canal; operculum small for the aperture, corneous, claw-shaped, edge notched. Lias ——. Genera: Strombus (Fig. [99], p. 200); Pereiraea (Miocene), Pteroceras (Fig. [277]; digitations of the outer lip very strong), Rostellaria (spire produced, anterior canal very long), Rimella, Pterodonta, Terebellum (base of shell truncate, spire short).