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). FAMILY 13. LIMACINIDAE, Gray. Dextral animals 

 with visceral mass and shell coiled "pseudo-sinistrally" (ultra-dextrally) ; 

 operculum with sinistral spiral ; pallial cavity dorsal. Genera Peraclis, 

 Forbes ; head proboscidiform, with symmetrical tentacles ; a ctenidium. 

 Limacina, Cuvier ; head much reduced ; the right tentacle larger than the 

 left (Fig. 63); British. FAMILY 14. CYMBULIIDAE, Cantraine. Adult 

 without shell ; a sub-epithelial pseudoconch formed by the connective 

 tissue ; pallial aperture ventral. Genera Cymhulia, PeVon and Lesueur ; 

 pseudoconch thick; foot with a median ventral filament (Fig. 151). 

 Cymtiuliopsis, Pelseneer ; pseudoconch thin, with a large cavity. Gleba, 



Cymbulia peroni, swimming, left-side view. I, position of the mouth, seen through the tin ; 

 1 1, the sub-epithelial pseudoconch ; III, visceral mass ; IV, pallial cavity ; V, posterior flagellum 

 of the foot ; VI, left tin. (After Delle Chiaje.) 



Forskal ; pseudoconch thin, with scarcely any cavity. Desmopterus, Chun ; 

 each fin with a posterior filament. FAMILY 1 5. CAVOLINIIDAE, 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 



