21 
CLITHON. 
Ciituon, De Moni/ort. 
Nerira, Linné, &c. 
Urcevs, Klein. 
CHARACTER GENERICUS. 
Testa libera, univalvis; spira regularis, depressa; umbilicus 
nullus; os subrotundatum ; columel/a acuta, subdentata 
aut dentata; dabium extertus tenue. 
AniMat fluviatile ; capite subrostrato; tentaculis duobus, 
oculis ad illorum basin externé. 
CLITHON. 
Shell free, univalve; spire regular, depressed; umbilicus 
none; mouth subrounded ; pillar sharp, subdentate or 
dentate ; external lip thin. 
Anima. with its head subrostrated, with two tentacules 
bearing eyes at their base externally. 
The genus Clithon differs from Theodoxis, (the type of 
which is the Nerita fluviatilis of Linné), in having its co- 
lumella with teeth. 
Some species of Clithon are armed with spines, others 
again are perfectly simple. The exact form of the tenta- 
cules of the Cithones has not been ascertained. It is pro- 
bable, judging by analogy, that the tentacules of the 
spined, and of the simple species, will be found to be dif- 
ferent. 
