Fig. 46.
A, Eolis papillosa (Lin.), dorsal view.

a, b, Posterior and anterior cephalic tentacles.

c, The dorsal “cerata.”

B, Tethys leporina, dorsal view.

a, The cephalic hood.

b, Cephalic tentacles.

c, Neck.

d, Genital pore.

e, Anus.

f, Large cerata.

g, Smaller cerata.

h, Margin of the foot.

C, Doris (Actinocyclus) tuberculatus (Cuv.), seen from the pedalsurface.

m, Mouth.

b, Margin of the head.

f, Sole of the foot.

sp, The mantle-like epipodium.

D, E, Dorsal and lateral view of Elysia (Actaeon) viridis.ep, epipodial outgrowths. (After Keferstein.)
Fig. 47.—Enteric Canal of Eolis papillosa. (FromGegenbaur, after Alder and Hancock.)

ph, Pharynx.

m, Midgut, with its hepatic appendages h, all of which are not figured.

e, Hind gut.

an, Anus.

Fig. 48.—Central Nervous System ofFiona (one of the Nudibranchia), showing a tendencyto fusion of the great ganglia. (From Gegenbaur,after Bergh.)

A, Cerebral, pleural and visceral ganglia united.

B, Pedal ganglion.

C, Buccal ganglion.

D, Oesophageal ganglion connected with, the Buccal.

a, Nerve to superior cephalic tentacle.

b, Nerves to inferior cephalic tentacles.

c, Nerve to generative organs.

d, Pedal nerve.

e, Pedal commissure.

e′, Visceral loop or commissure (?).

Fig. 49.—Cavolinia tridentata, Forsk. from the Mediterranean, magnified two diameters. (From Owen.)
a, Mouth. b, Pair of cephalic tentacles. C, C, Pteropodial lobes of the foot. d, Median web connecting these. e, e, Processes of the mantle-skirt reflected over the surface of the shell. g, The shell enclosing the visceral hump. h. The median spine of the shell.
Fig. 50.—Shell of Cavolinia tridentata, seen from the side.
f, Postero-dorsal surface. g, Antero-ventral surface. h, Median dorsal spine. i, Mouth of the shell.

Fam. 1.—Actaeonidae. Cephalic shield bifid posteriorly; margins of foot slightly developed; genital duct diaulic; visceral commissure streptoneurous; shell thick, with prominent spire and elongated aperture; a horny operculum. Actaeon, British. Solidula. Tornatellaea, extinct. Adelactaeon. Bullina. Bullinula.

Fam. 2.—Ringiculidae. Cephalic disk enlarged anteriorly, forming an open tube posteriorly; shell external, thick, with prominent spire; no operculum. Ringicula. Pugnus.

Fam. 3.—Tornatinidae. Margins of foot not prominent; no radula; shell external, with inconspicuous spire. Tornatina, British. Retusa. Volvula.

Fam. 4.—Scaphandridae. Cephalic shield short, truncated posteriorly; eyes deeply embedded; three calcareous stomachal plates; shell external, with reduced spire. Scaphander, British. Atys. Smaragdinella. Cylichna, British. Amphisphyra, British.

Fam. 5.—Bullidae. Margins of foot well developed; eyes superficial; three chitinous stomachal plates; shell external, with reduced spire. Bulla, British. Haminea, British.

Fam. 6.—Aceratidae. Cephalic shield continuous with neck; twelve to fourteen stomachal plates; a posterior pallial filament passing through a notch in shell. Acera, British. Cylindrobulla. Volutella.

Fam. 7.—Aplustridae. Foot very broad; cephalic shield with four tentacles; shell external, thin, without prominent spire. Aplustrum. Hydatina. Micromelo.