741 



SEMIPHYLLIDIANS. 



SEMNOPITHECU3. 



713 



P. reticulatus. This species is not noticed in the last edition of 

 Lamarck. 



There are about 20 species of Pleurobranchus. 



Pleurobranchus rtticulattu, seen from above. (Gueiin.) 



Spiricella (Rang) is a fossil genus. The shell is very much flattened, 

 elongated, bent (arquee), with sharp edges ; apex spiral, sinistrorsal, 

 horizontal, situated backwards and to the left, open on the lower 

 surface; an indistinct impression, but appeal iug to occupy the pos- 

 terior part of the shell, where it shows itself nearly parallel to the 

 border. 



The only species is S. Unguiculiu. 



Umbrella, Lam. (Gastroptaj:, De Elainv.). Animal oblong, very 

 much depressed, convex above, very flat and fleshy below. Mantle 

 not much extended. Head not distinct; mouth situated at the bottom 

 of a narrow and deep notch in front of the foot, which has thick edges, 

 and is raised all round. Four tentacles : two superior, truncated, slit, 

 and lamellose, as it were, internally ; two smaller, in form of pedicu- 

 lated crests, on each side of the mouth. Foot very large, spreading 

 out on all sides, smooth and flat Kranchirc foliaceous, disposed in a 

 cordon all along the right side, and reaching even a little to the left in 

 passing by the front; anus in the form of a small tube behind the 

 branchiae. Organs of generation very much approximated, situated to 

 the right and forwards. 



Shell external, calcareous, very much depressed, nearly entirely 

 flat, irregularly circular, slightly convex above and concave below ; 

 apex excentric, conical, and slightly inflected ; concentrically striated 

 and radiated ; edge trenchant, fixed to the dorsal part, which it covers. 

 (Rang.) 



The species are littoral. Depth, &c., much the same as in Pleura- 

 Itranchut. 



Two species only appear to be known V. Indica and V. Mediter- 

 ranca. 



U. Medticrranea has the umbrella with a flattened shell ; the disc of 

 the lower surface not radiated. 



Umbrtlta Mcditcrranea, with the shell in the proper position, 

 a, shell; ft, gilU; r, head, viewed from above. (1'killppi.) 



Shell of Umbrella Indica. 

 a, inside ; &, outside. 



Siplionaria, Sowerby. Animal oval, sub-depressed ; the head sub- 

 divided into two equal lobes, without tentacles or apparent eyes. 

 Borders of the mantle crenulated. A branchia in form of a squara 

 membrane, in the sinus formed at the right, between the foot and the 

 mantle. 



Shell patelloid, elliptical, with the apex well marked, slightly to the 

 left and posterior ; a sort of canal or gutter on the right side ; mus- 

 cular impression of a horse-shoe shape, the right lobe divided into two 

 by the canal. (De Blainv.) 



Shell of Sipltnnarin S'i>ho. 

 a, outside ; 6, inside. 



Small species of Siphonaria, with the animal in the shell. 

 1, lateral view ; 2, ventral view ; a, breathing aperture ; J, head j c, mantle. 



The species are littoral. Depth, &c., much the same as in Pleura- 

 branchut and Umbrella. They are found in Brazil, the West Indies, 

 Senegal, and Tristan d'Acunha. (Sowerby.) 



M. Deshayes, in his Tables, makes the number of living species of 

 Siphonaria 21, aud that of the fossil species (tertiary) 3. In the last 

 edition of Lamarck the number of living species recorded is 19. 



SEMNOPITHE'CUS, F. Cuvier's name for a genus of Monkeys. 



The canines are much longer than the incisors ; head round ; facial 

 angle more open than that of the Orang's ; face flat. Limbs very long 

 iu proportion to the body ; anterior thumbs very short Cheek- 

 pouches small or null. Callosities. Tail very long and slender. 



Dental Formula: Incisors, 1; Canines. * ; Molars, 5 -^ = 32. 

 4 1 1 6 5 



F. Cuvier observes that the canines are often much larger than 

 the rest of the teeth, and consequently than they are hero represented. 

 This is exemplified in the case of S. Mawue. 



