226 Lamarck's Genera of Shells, 



closed between two equal shields. Branchiae on the right side, 

 inserted in the canal, and disposed in series, on the two faces 

 of a longitudinal lamina. Mouth anterior, proboscis-shaped, 

 situated underneath. Two cylindrical, hollow tentacula, with 

 an external longitudinal fissure, attached to the lamina which 

 covers the mouth. Aperture of the organs of generation in front 

 of the branchial lamina ; anus behind ; both on the right side. 



Shell internal, dorsal, thin, flattened, often oblique-oval. 



One species. Pleurobranchus Peronii. 



No further description. 



Indian Seas. PI. VII. Fig. 113. 



2. Umbrella. 



Body very thick, subovate, furnished with a dorsal shell ; foot 

 very large, prominent, smooth and flat on the under part, notched 

 before, posteriorly attenuated. Head not distinct ; mouth at 

 the bottom of a funnel-shaped cavity, situated in the anterior 

 sinus of the foot. Four tentacula ; two superior, thick, short, 

 truncated, with a fissure on one side, internally, transversely sub- 

 lamellar ; two others thin, cristate, pedunculated, inserted at 

 the sides of the mouth. Branchia; foliaceous, arranged in series 

 between the foot and the border of the mantle, through the 

 whole length of the right side, both anterior and lateral. Anus 

 behind the posterior extremity of the branchiae. 



Shell external, orbicular, rather irregular, almost flat, slightly 

 convex above, white ; apex small, near the middle ; margin sharp ; 

 internal face slightly concave, presenting a callous, colourless 

 disk, depressed in the centre, and surrounded by a smooth 

 border. 



M. de Blainville, who has described the animal of the um- 

 brella under the name of gastroplax, says, that its " shell has 

 been found adhering to the inferior face of the animal." M. 

 Mathieu, however, who has seen the species alive, at the Isle of 

 France, asserts that the shell is dorsal. 



Type. Umbrella Indica t. (Patella umbellata, Gmel.) 



* Our figure is copied from that in ihs AnnalesduMus&um, V. PI. XVIII. 



Fig, 1 and 2. 



t Imlian umbrtUa, coaunonly ceilled the Chinat parasol. 



