Fig. 270.—Monodonta canalifera Lam., New Ireland. (After Quoy and Gaimard.)
Fam. 5. Trochidae.—Snout short, broad, frontal lobes often present, epipodial line furnished with cirrhi; shell nacreous, variously spiral, operculum corneous, multispiral, nucleus central (Fig. [182], p. 268). Silurian——. (i.) Trochinae.—Frontal lobes present, lateral teeth (= side centrals) 5 only, no jaws, peristome incomplete. Principal genera: Trochus (subg. Cardinalia, Tectus, Infundibulum, Clanculus), Monodonta (subg. Diloma), Cantharidus (subg. Bankivia, Thalotia), Gaza (subg. Microgaza), Callogaza, Bembix, Chlorostoma. (ii.) Gibbulinae.—Frontal lobes and jaws present, laterals often more than 5, peristome incomplete. Principal genera: Gibbula (subg. Monilia, Aphanotrochus, Enida), Minolia, Circulus, Trochiscus, Livona, Photinula, Margarita, Solariella, Calliostoma, Turcica, Basilissa, Euchelus (subg. Olivia, Perrinia). (iii.) Delphinulinae.—No frontal lobes, jaws present; shell solid, surface spirally lirate, scaly, spinose, umbilicate, peristome continuous. Single genus, Delphinula. (iv.) Umboniinae.—Eyes pedunculate, left tentacle attached to a frontal appendage, mantle reflected over edge of aperture, lateral teeth 6 on each side; shell polished, peristome incomplete, umbilicus generally closed by a callosity. Principal genera: Umbonium, Ethalia, Isanda, Camitia, Umbonella, Chrysostoma.
Fig. 271.—Phasianella australis Gmel., Australia.
Fam. 6. Turbinidae.—Epipodial line with slender cirrhi, snout broad, short, eyes pedunculate at outer base of tentacles, a frontal veil between tentacles; shell turbinate, solid, aperture continuous, operculum solid, calcareous, usually paucispiral, convex exteriorly (Fig. [182], p. 268). Silurian——. (i.) Phasianellinae.—Shell bulimoid, polished, not nacreous, coloured in patterns, aperture oval. Single genus, Phasianella (Fig. [271]). (ii.) Turbininae.—Shell very solid, nacreous within, aperture circular or long oval. Principal genera, Turbo, whorls rounded above and below, spines, if present, becoming more prominent with age, operculum smooth or granulose, nucleus sub-central; subg. Callopoma, Ninella, Marmorostoma, Sarmaticus, Prisogaster; Astralium, whorls flattened above and below, spines, if present, becoming less prominent with age, operculum oblong, often excavated at centre, last whorl large, nucleus marginal or sub-marginal; subg. Lithopoma, Imperator, Guildfordia, Bolma, Cyclocantha, Uvanilla, Cookia, Pomaulax, Pachypoma. (iii.) Cyclonematinae.—Shell nacreous, umbilicate, operculum conical outside, whorls scalariform. Principal genera: Cyclonema, Horiostoma (?), Amberleya (Silurian to Lias). (iv.) Leptothyrinae.—Shell small, solid, depressed, operculum nearly flat, nucleus sub-central. Genera: Leptothyra, Collonia (?).
Fam. 7. Neritopsidae.—Tentacles wide apart, long, eyes on short peduncles at the outer base; shell solid, neritiform or naticoid, aperture semi-lunar or oval; operculum (Fig. [183], p. 269) thick, calcareous, non-spiral, exterior face smooth, interior face divided into two unequal parts, with a broad median appendage. Devonian——. Principal genera: Neritopsis (one recent species), Naticopsis (Devonian to Miocene).
Fam. 8. Macluritidae.—Shell discoidal, whorls few, longitudinally grooved behind, right side convex, deeply umbilicated, left side flat; operculum very thick, nucleus excentrical, internal face with two apophyses, one very large. The general appearance is more that of an inequivalve bivalve, such as Requienia, than of a spiral gasteropod. Palaeozoic——. Single genus, Maclurea.
Fam. 9. Neritidae.—Snout short, tentacles long, eyes pedunculate at their outer base, branchia triangular, free at the front end, epipodium without cirrhi, penis near the right tentacle; shell solid, imperforate, turbinate to almost patelliform, spire short, internal partitions absorbed (p. [168]), columellar region broad, edge simple or dentate, operculum calcareous, spiral or non-spiral, with prominent apophyses on the interior face, one of which locks behind the columellar lip. Jurassic——. Principal genera: Nerita (Fig. [13], p. 17); Neritina (chiefly brackish water and fluviatile), sub-genus Clithon, usually coronated with spines; Velates (Tertiary), Neritoma (Jurassic), Deianira (Cretaceous), Septaria (= Navicella), shell more or less narrowly patelliform, with terminal apex, aperture very large, with a broad columellar septum, operculum too small for the aperture, more or less covered by the integument of the foot; fluviatile only; Pileolus (Jurassic to Cretaceous).
Fam. 10. Hydrocenidae.—Branchia replaced by a pulmonary chamber, eyes at the outer base of the tentacles, marginals of the radula very oblique, centrals often wanting; shell small, conical, whorls convex, operculum calcareous, with a prominent apophysis. Recent. Principal genera: Hydrocena, Georissa.
Fam. 11. Helicinidae.—Branchia replaced by a pulmonary chamber, heart with one auricle; shell globular, with a short spire, internal partitions absorbed; operculum without apophysis. Carboniferous——. Principal genera: Helicina (Fig. [18]B, p. 21; subg. Alcadia, Schasicheila, Heudeia, Calybium), Eutrochatella (subg. Lucidella), Stoastoma, Bourcieria, Dawsonella (Carboniferous).