Fam. 8.—Pleurophyllidae. Anterior tentacles in the form of a digging shield; mantle without appendages, but respiratory papillae beneath the mantle-border. Pleurophyllidia.
Fam. 9.—Dermatobranchidae. Like the last, but wholly without branchiae. Dermatobranchus.
Tribe 4.—Elysiomorpha. Liver ramifies in integuments and extends into dorsal papillae, but there are no cnidosacs. Genital duct always triaulic, and male and female apertures distant from each other. No mandibles, and radula uniserial. Never more than one pair of tentacles, and these are absent in Alderia and some species of Limapontia.
| Fig. 55.—Dorsal and Ventral View of Pleurophyllidia lineata (Otto), one of the Eolidomorph Nudibranchs. (After Keferstein.) |
| b, The mouth. l, The lamelliform sub-pallial gills, which (as in Patella) replace the typical Molluscan ctenidium. |
Fam. 1.—Hermaeidae. Foot narrow; dorsal papillae linear or fusiform, in several series. Hermaea, British. Stiliger. Alderia, British.
Fam. 2.—Phyllobranchidae. Foot broad; dorsal papillae flattened and foliaceous. Phyllobranchus. Cyerce.
Fam. 3.—Plakobranchidae. Body depressed, without dorsal papillae, but with two very large lateral expansions, with dorsal plications. Plakobranchus.
Fam. 4.—Elysiidae. Body elongated, with lateral expansions; tentacles large; foot narrow. Elysia, British. Tridachia.
Fam. 5.—Limapontiidae. No lateral expansions, and no dorsal papillae; body planariform; anus dorsal, median and posterior. Limapontia, British. Actaeonia, British. Cenia.
Order 2 (of the Euthyneura).—Pulmonata. Euthyneurous Gastropoda, probably derived from ancestral forms similar to the Tectibranchiate Opisthobranchia by adaptation to a terrestrial life. The ctenidium is atrophied, and the edge of the mantle-skirt is fused to the dorsal integument by concrescence, except at one point which forms the aperture of the mantle-chamber, thus converted into a nearly closed sac. Air is admitted to this sac for respiratory and hydrostatic purposes, and it thus becomes a lung. An operculum is present only in Amphibola; a contrast being thus afforded with the operculate pulmonate Streptoneura (Cyclostoma, &c.), which differ in other essential features of structure from the Pulmonata. The Pulmonata are, like the other Euthyneura, hermaphrodite, with elaborately developed copulatory organs and accessory glands. Like other Euthyneura, they have very numerous small denticles on the lingual ribbon. In aquatic Pulmonata the osphradium is retained.