412 TROCIIIN/E. 



Genus LivoNA, Gray. 



Lateral membrane of the foot with nmnerous, com- 

 pound appendages. 



Shell conoidal, sub-globose, smooth, solid, umbilicated, 

 umbilicus moderate, with a tooth-shaped process at the 

 entrance ; aperture circular, peritreme simple, thin, 

 acute. 



Syn. Turbo, Adans., not Linn. Tigris, Klem^ not 

 Linn. Meleagris, Monff., not Linn. Meleager, Grijf. 

 Cittarium, Pltil. Trochus, Sicains., not Linn. 



Ex. L. pica, Linmeus, pi. 46, fig. 6. Operculum, 

 L. pica, fig. 6, a, 6, b. Shell, L. pica, fig. (3, c. 



The appendages of the lateral membrane of the foot 

 are compound in this genus, while in the other genera of 

 TrochidcB they are, as far as we know, simple. 



Genus TROCHUS, Linnaeus. 



Shell conical, axis imperforate, last whorl angulated at 

 the periphery ; columella superiorly spirally twisted, form- 

 ing a canal, anteriorly simple, straight, ending in a 

 point. 



Ea\ T. Niloticus, Linnceus, pi. 46, fig. 7. Oper- 

 culum, T. Niloticus, fig. 7, a. Shell, T. Niloticus, fig. 7, b. 



The genus Trochus, as strictly defined, comprises but 

 few species, all inhabitants of equatorial countries. The 

 axis of the shell is not truly perforated, but the colu- 

 mella being twisted abruptly on itself at the hind part, 

 gives the appearance of a false umbilicus, and produces 

 the kind of canal which serves to distinguish the genus. 



