Fam. 6.—Bornellidae. Dorsum furnished on either side with papillae, at the base of which are ramified appendages. Bornella.

Fam. 7.—Lomanotidae. Body flattened, the two dorsal borders prominent and foliaceous. Lomanotus, British.

Tribe 2.—Doridomorpha. Body externally symmetrical; anus median, posterior, and generally dorsal, surrounded by ramified pallial appendages, constituting a secondary branchia. Liver not ramified in the integuments. Genital duct triaulic. Spicules present in the mantle.

Fig. 53.—Halopsyche gaudichaudii,Soul. (From Owen.) Much enlarged; the body-wall removed.

a, The mouth.

c, The pteropodial lobes of the foot.

f, The centrally-placed hind-foot.

d, l, e, Three pairs of tentacle-like processes placed at the sides ofthe mouth, and developed (in all probability) from the fore-foot.

o′, Anus.

y, Genital pore.

k, Retractor muscles.

o and p, The liver.

u, v, w, Genitalia.

Fig. 54.—Anculacristata, one of the pygobranchiate Opisthobranchs (dorsal view). (From Gegenbaur,after Alder and Hancock.)

a, Anus.

br, Secondary branchia surrounding the anus.

t, Cephalic tentacles.

External to the branchia are seen ten club-like processes ofthe dorsal wall, these are the “cerata” which are characteristicallydeveloped in another suborder of Opisthobranchs.

Fam. 1.—Polyceratidae. A more or less prominent frontal veil; branchiae non-retractile. Euplocamus. Polycera, British. Thecacera, British. Aegirus, British. Plocamopherus. Palio. Crimora. Triopa, British. Triopella.

Fam. 2.—Goniodorididae. Mantle-border projecting; frontal veil reduced, and often covered by the anterior border of the mantle. Goniodoris, British. Acanthodoris, British. Idalia, British. Ancula, British. Doridunculus. Lamellidoris. Ancylodoris, the only fresh-water Nudibranch, from Lake Baikal.

Fam. 3.—Heterodorididae. No branchia. Heterodoris.

Fam. 4.—Dorididae. Mantle oval, covering the head and the greater part of the body; anterior tentacles, ill-developed; branchiae generally retractile. Doris, British. Hexabranchus. Chromodoris.

Fam. 5.—Doridopsidae. Pharynx suctorial; no radula; branchial rosette on the dorsal surface, above the mantle-border. Doridopsis.

Fam. 6.—Corambidae. Anus and branchia posterior, below the mantle-border. Corambe.