CONCHOLOGY. 



91 



P, amcena.* , P. alveus * 



P. alternata.* P. Candida.* 



5. Genus UmbreUa. PI. IX. 



Aniinal. Body very thick and oval, provided with a dorsal 

 shell ; foot large, smooth, and flat, surrounded by a border, ante- 

 riorly notched, attenuated behind ; head indistinct ; four tenta- 

 cula, the two upper ones thick, short, and truncated, the other 

 two thin, and shaped like pedunculated crests ; having foliaceous 

 branchiae. 



Shell. External, orbicular, subirregular, nearly flat, slightly 

 convex above, white, with apex near the middle ; margin acute, 

 internal surface rather concave ; having a callous disk, coloured, 

 depressed in the centre, surrounded by a smooth border. Inhabits 

 the Indian Ocean. Two species. 



Umbrella Indica. Umbrella Mediterranea. 



6. Genus PlenrobrancJnts. PI. IX. 



Animal. Body creeping, fleshy ; mantle and foot expanded ; 

 branchise placed on the right side ; cloak enveloping the shell ; 

 neck short, contracted in some species, with an emarginate front, 

 exhibiting the commencement of the inferior tentacula, the upper 

 ones tubular and cloven ; gills at the edge of the dorsal plait, 

 mouth provided with a short, retractile proboscis. 



Shell. Depressed, oval, oblong, concentrically wrinkled, almost 

 entirely open, rounded and convoluted ; the vertex with a single 

 turn. Inhabits the coast of Devonshire in England Two 

 species. 



Pleurobranchus Peronii. Pleurobranchus Laqueare. 



FAMILY III. 

 Caltptracea. Seven genera. 

 1. Genus Parmophoriis. PI. IX. 



Animal. Body creeping, thick, oblong ovate, broad behind, 

 obtuse at the extremities ; border of the mantle cleft before, and 



