The Cambridge natural history . orls flattened above andbelow, spines, if present, becoming less prominent with age,operculum oblong, often excavated at centre, last whorl large,nucleus marginal or sulvmarginal; subg. ZitJiopoma, Impcrator,Guildfordia, Bohna, Cydocantha, UvaniUa,Cookia, Pomaidax, Pacliypoma. (iii.) Cyclo-nematinae.—Shell nacreous, umbilicate,oper-culum conical outside, whorls genera; Cyclonema, Horiostoma,(?) Amberleya (Silurian to Lias), (iv.) LcjJto-thyrinae. — Shell small, solid, depressed,operculum nearly Hat, nucleus ; Lcptothyra,
The Cambridge natural history . orls flattened above andbelow, spines, if present, becoming less prominent with age,operculum oblong, often excavated at centre, last whorl large,nucleus marginal or sulvmarginal; subg. ZitJiopoma, Impcrator,Guildfordia, Bohna, Cydocantha, UvaniUa,Cookia, Pomaidax, Pacliypoma. (iii.) Cyclo-nematinae.—Shell nacreous, umbilicate,oper-culum conical outside, whorls genera; Cyclonema, Horiostoma,(?) Amberleya (Silurian to Lias), (iv.) LcjJto-thyrinae. — Shell small, solid, depressed,operculum nearly Hat, nucleus ; Lcptothyra, Collonia (?). Fam. 7. Neritopsidae.—Tentacles wideapart, long, eyes on short pedvmcles at theouter base; shell solid, neritiform or naticoid,aperture semi-lunar or oval ; operculum(Fig. 183, p. 269) thick, calcareous, non-spiral, exterior face smooth, interior facedivided into two unequal parts, with a broad median appendage. Devonian . Principal genera : Neri- topsis (one recent species), Naticoims (Devonian to Miocene).. Fig. 271.—PhasianeUa aus-tralis Gmel., Australia. AIO DIOTOCARDIA RHIPIDOGLOSSA chap. Fam. 8. Macluritidae.—Shell discoidal, whorls few, longi-tudinally grooved behind, right side convex, deeply unibilicated,left side flat; operculum very thick, nucleus excentrical, internalface with two apophyses, one very large. The general appearanceis more that of an inequivalve bivalve, such as Eequienia, than ofa spiral gasteropod. Palaeozoic . Single genus, Maclurea. Fam. 9. Neritidae.—Snout short, tentacles long, eyes pedun-culate at their outer base, branchia triangular, free at the frontend, epipodiurn without cirrhi, penis near the right tentacle;shell solid, imperforate, turbinate to almost patellifoiin, spireshort, 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 . Princi
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
