Lamarck's Genera of Shells. 253 



Shell orbicular, convex, conoid al, very smooth, pale flesh- 

 colour ; numerous undulated, brown, longitudinal lines ; whorls 

 contiguous ; lower face white. Mediterranean. PI. VIII. Fig. 

 165. 5 Species. 



3. Trochus*. 

 Shell conical, spire elevated, sometimes rather depressed ; 

 periphery more or less angular, often thin and acute. Aperture 

 depressed transversely ; margins disunited at the upper part. 

 Columella arched, more or less prominent at the base. An 

 operculum. 



Many trochi have a brilliant pearly surface, and several 

 have longitudinal ribs, which, we believe, are never found in 

 the turbo. 



Type. Tiochus imperialist. (Idem. Gmel.) 



Shell orbicular-conoidal, apex obtuse, brown inclining to 

 violet above, white below; transverse furrows, imbricate- 

 squamose ; whorls convex, turgid, radiated with a squamosa 

 margin ; squamae complicate ; umbilicus funnel-shaped. — South 

 Seas. PI. VIII. Fig. 166. 69 Species. 

 4. MonodontaJ. 

 Shell oval or conoidal. Aperture entire, round; margins 

 disunited at the upper part. Columella arched, truncated at 

 the base. Operculum orbicular, thin, horny. 



Distinguisiied from trochus chiefly by the more circular form 

 of the mouth ; from turbo by the columella being truncated at 

 the base, and forming a characteristic dentiform projection in 

 the aperture. 



Type. Monodonta pagodus\. (Turbo pagodus. Lzwn.) 



Shell obliquely conical, imperforate, tubercular, ribbed longi- 

 tudinally, transversely furrowed, brownish grey; ribs termi- 

 nating in long, compressed tubercles beyond the margin of 

 the spires ; lower face white, with concentric furrows, pimpled. 

 Indian Ocean. PI. VIII. Fig. 167. 25 Species. 

 5. Turbo ||. 

 Shell conoidal, or subturrited ; periphery never compressed ; 



» A child's lop. ♦ hnpcrial. 



t From (Ltovcc one, and oJac a tooth. § Pagoda. \\ A ureath. 



