THE GASTROPODA 175 
EEE 
is extremely reduced. The phylogenetic relationships between the Nudi- 
branchs and Tectibranchs are clearly exhibited by the organisation of the 
Pleurobranchomorpha, in which there is neither a pallial cavity nor an 
osphradium, and the respiration is largely pallial. The shell is altogether 
absent in Pleurobranchaea ; the nervous system is concentrated on the 
dorsal side of the oesophagus ; spicules and cnidocysts are found in the 
dorsal integuments. The mantle of the Doridomorpha is completely 
homologous with that of the Pleurobranchidae, and is in no wise to be 
regarded as an epipodium reflected over the dorsal surface of the body, 
Ve 
Fia. 159. 
Nervous system of Goniodoris, dorsal view. a, cerebro-pleural ganglion, with eye and oto- 
eyst; b, pedal ganglion ; ¢, sub-cerebral commissure ; d, visceral commissure ; @, visceral nerve ; 
: genital nerve ; g; penial nerve ; ji, pallial nerve ; 7, tentacular nerve and ganglion ; j, stomato- 
gastric ganglion. 
TRIBE 1. TRITONIOMORPHA. 
Nudibranchia in which the liver is wholly or partially contained in 
the visceral mass. The anus is lateral, on the right side. There are 
generally two rows of ramified dorsal appendages (Fig. 83, II). The genital 
duct is diaulic; the male and female orifices contiguous. Famity 1. 
TrrirontpArE, Adams. The anterior tentacles form a frontal veil; the 
foot rather broad. Genera—Tritonia, Cuvier; stomach without horny 
plates ; British (Fig. 83). Marionia, Vayssiere ; stomach with horny plates. 
Famity 2. Scytiarmar, Alder and Hancock. No anterior tentacles ; 
dorsal appendages broad and foliaceous ; foot very narrow ; stomach with 
horny plates. _Genus—Scyllaea, Linnaeus ; pelagic. Faminy 3. PHYLLIR- 
HOIDAE, Adams. No anterior tentacles and no dorsal appendages ; body 
laterally compressed ; transparent natatory forms. Genus—Phyllirhoé, 
Péron and Lesueur (Fig. 161). Famimy 4. Trernyimpar, Alder and 
Hancock. Head broad, surrounded by a funnel-shaped velum or hood ; 
no radula; dorsal appendages foliaceous. Genera—Tethys, Linnaeus ; 
foot broad ; no mandibles (Fig. 160, B). Melibe, Rang ; foot narrow ; 
mandibles present. Faminy 5. Denpronotipar, Alder and Hancock. 
Anterior tentacles forming a scolloped frontal veil ; dorsal appendages and 
tentacles similarly ramified. Genera—Dendronotus, Alder and Hancock ; 
