THE GASTROPODA 181 
phyllidia, but wholly devoid of “branchiae.”’ Genus—Dermatobranchus, 
van Hasselt. 
TRIBE 4. ELYSIOMORPHA. 
Nudibranchia in which the liver ramifies in the integuments and 
extends into the dorsal papillae. The genital duct is always triaulic, 
and the male and female orifices are distant (Fig. 105). The gonad is 
divided into spheroidal hermaphrodite lobules. There are no mandibles, 
and the radula is uniserial. There is never more than one pair of tentacles, 
and these are wanting in Alderia and some species of Limapontia. The 
otocysts contain each a single otolith. 
Famity 1. Hermarrpar, Adams. Foot narrow; dorsal papillae 
without nematocysts, linear or fusiform, and disposed in several series. 
Genera—Hermaea, Loven ; rhinophores split throughout their length ; 
dorsal papillae linear ; anus antero-dorsal ; British. Stiliger, Ehrenberg ; 
rhinophores simple ; dorsal papillae fusiform or ovoid ; anus antero-dorsal. 
Alderia, Allman; anus median and posterior; no tentacles; dorsal 
papillae linear; inhabitants of brackish waters; British. Faminy 2. 
PHYLLOBRANCHIDAE, Bergh. Foot broad; dorsal papillae without 
TTR Sigg oo 
Fic. 170. 
Cenia cockst, left-side view, magnified a, anus. (After Hancock.) 
nematocysts, flattened and foliaceous. Genera—Phyllobranchus, Alder 
and Hancock ; foot simple ; anus latero-dorsal. Cyerce, Bergh; ventral 
part of the foot divided transversely ; anus median. FAminy 3. PLaKo- 
BRANCHIDAE, d’Orbigny. Body depressed, without dorsal papillae, but with 
two very large lateral expansions with dorsal plications ; head flattened ; 
eyes approximated. Genus—Plakobranchus, van Hasselt. Faminy 4. 
EtysiipAk, Adams. Body elongated, with lateral expansions; head 
rounded and eyes separated ; tentacles large; foot narrow. Genera 
Elysia, Risso ; British (Fig. 160, D, E). Tridachia, Deshayes. Famtty 5. 
LIMAPONTIIDAE, Adams. No lateral expansions of the body and no dorsal 
papillae ; body planariform ; anus dorsal, median, and posterior. Genera 
—Limapontia, Johnston ; no tentacles ; head and body devoid of crests ; 
British. Actaeonia, Quatrefages; head carinated laterally; British. 
Cenia, Alder and Hancock ; head with two long tentacles (Fig. 170). 
ORDER 2. Pulmonata, Cuvier. 
Euthyneura with a pallial cavity but no ctenidium. The pallial 
aperture is diminished by the fusion of the mantle border with the 
neck, and reduced to a comparatively small contractile orifice at its 
posterior extremity (Fig. 177, V). The pallial cavity and shell are 
