TRIBE III. PLEUROBRANCHOIDEA. 



Dorsal region covered by a large shield-like mantle, or 

 notaeum. Shell external, internal or absent. Head distinct, with 

 two pairs of tentacles. A single ctenidium on the right side, 

 between the mantle and foot. Foot without parapodia. Genital 

 duct diaulic, the male and female apertures contiguous. Visceral 

 commissure short. 



Family PLEUROBRANCHIDAE. 



Mantle fleshy, stiffened by spicules, concealing wholly or 

 partly the delicate haliotiform shell, if developed at all. Anterior 

 tentacles united to form a frontal veil, posterior tentacles, or 

 rhinophores, auriculate. Foot flattened, large. Radula multiserial, 

 with no rhachidian teeth. Mandibles well developed, composed 

 of many oblong plates arranged in tesselated pattern. 



Genus PLEUROBRANCHUS Cuvier, 1805. 



Pleurobranchus, Cuvier. Memoire sur la Phyllidie et sur le 



Pleurobranche. Annales du Museum d'Histoire Na- 



turelle, V, 1805, p. 266-276, PI. 18, Figs. 1-6. 

 Berthella, Blainville. Manuel de Malacologie. 1825, p. 469, 627, 



PI. XLIII, Fig. i. 

 Pleurobranchus, Pilsbry. Tryon's Manual of Conchology, XVI, 



1896, p. 191. 

 Pleurobranchus, Vayssiere. Monographic des Pleurobranchides. 



Ann. des Sciences Naturelles, Zoologie. Ser. 8, T. VIII, 



1898, p. 279. 

 Pleurobranchus, Bergh. Malacologische Untersuchungen, IV. 



i, 3, in Semper's Reisen im Archipel der Philippinen, 



VII, 1898, p. 117. 



Body elliptical, mantle more or less developed, its borders 

 free, the anterior border more or less emarginate ; shell internal, 

 calcareous or subcalcareous. Rhachis of ctenidium smooth. Male 

 and female genital openings contiguous, or almost united. Mandi- 

 bles made up of flattened, closely set elements. 



