The Cambridge natural history . Frfi. 17.—Two rows of the radula of Cijdophorus sp., India, x 40, On the other hand, the Helicinidae, Hydrocenidae, andProserpinidae are equally closely related to Neritina. TheProserpinidae (restricted to the Greater Antilles, Central Americaand Venezuela) may perhaps be regarded as the ultimate termof the series. They have lost the characteristic operculum,wliicli in their case is replaced by a number of folds or lamellaein the interior of the shell. It has already been noticed howone group of Neritina {Neritodryas) occurs normally out of thewater. This group
The Cambridge natural history . Frfi. 17.—Two rows of the radula of Cijdophorus sp., India, x 40, On the other hand, the Helicinidae, Hydrocenidae, andProserpinidae are equally closely related to Neritina. TheProserpinidae (restricted to the Greater Antilles, Central Americaand Venezuela) may perhaps be regarded as the ultimate termof the series. They have lost the characteristic operculum,wliicli in their case is replaced by a number of folds or lamellaein the interior of the shell. It has already been noticed howone group of Neritina {Neritodryas) occurs normally out of thewater. This group furnishes a link between the fresh-water andland forms. It is interesting to notice that here we have themost perfect sequence of derivatives; Nerita in the main a. Fkj. 18.—A, Neritina reticularis Sowb., Calcutta (brackish water) ; B, Helicinaneritella Lam., Jamaica (land) ; C, Proser})ina [Ceres) eolina Duel., Central America(hmd). piirely marine form, with certain species occurring also inlirackish water; Neritina in the main fresh-water, but somespecies occurring on the muddy shore, others on dry land:Helicina the developed land form; and finally Proseiyina, anaberrant derivative which has lost the- operculum.^ One step even further (or perhaps it slioukl be termed a branch derivative) isseen in the genus Smaraydia, which is probably a Neritina whicli lias resumed apurely marine habit of life. 2 2 ORIGIN OF LAND PULMONATA Gasteropoda.—(2) Fulmonata. The origin of these, thebulk of the land fauna, must at present be regarded as a problemnot yet finally solved. Some authorities, as we have seen, regardthem as derived from the Nudibranchiate, others, probably morecorrectly, from the Tectibranchiate Opisthobranchs. The first known members of
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
