170 THE GASTROPODA 
side; two pairs of tentacles; Mediterranean. Lophocercus, Krohn; parapodia 
undivided and applied to the shell ; a single pair of tentacles ; Mediter- 
ranean (Fig. 150). Famity 13. Limacrnipar, Gray. Dextral animals « 
with visceral mass and shell coiled “pseudo-sinistrally” (ultra-dextrally) ; 
operculum with sinistral spiral ; pallial cavity dorsal. Genera—VPeraclis, 
Forbes ; head proboscidiform, with symmetrical tentacles ; a ctenidium. 
Limacina, Cuvier ; head much reduced ; the right tentacle larger than the 
left (Fig. 63); British. Faminty 14. CympuLupas, Cantraine. Adult 
without shell; a sub-epithelial pseudoconch formed by the connective 
tissue ; pallial aperture ventral. Genera—Cymbulia, Péron and Lesueur ; 
pseudoconch thick ; foot with a median ventral filament (Fig. 151). 
Cymbuliopsis, Pelseneer ; pseudoconch thin, with a large cavity. Gleba, 
Fic. 151. 
Cymbulia peroni, swimming, left-side view. I, position of the mouth, seen through the fin ; 
II, the sub-epithelial pseudoconch ; III, visceral mass ; IV, pallial cavity ; V, posterior flagellum 
of the foot; VI, left fin. (After Delle Chiaje.) 
Forskal ; pseudoconch thin, with scarcely any cavity. Desmopterus, Chun ; 
each fin with a posterior filament. Faminy 15. Cavoninipa®, d’Orbigny. 
Visceral mass and shell not coiled, symmetrical; pallial aperture ventral. 
Genera—Cavolinia, Abildgaard ; visceral mass and shell more or less 
flattened dorso-ventrally (Fig. 153) ; pallial appendages present which pass 
through lateral fissures in the shell. Clio, Browne; mantle without 
projecting appendages ; shell not septate ; universally distributed (Fig. 152). 
Cuvierina, Boas ; shell with a posterior septum ; circular in section. The 
three last families form the group formerly known as “ Thecosomatous 
Pteropods.” These animals are characterised, in contrast to other allied 
Mollusca, by the foot, which is entirely transformed into two anterior 
symmetrical fins ; by the existence of a mantle and mantle-cavity ; by the 
absence of eyes in the adult; by the absence of a ctenidium, except in 
