( 52) 
DIVISION XV. HEMICYCLOSTOMATA. 
GENERA. 
Nenita, Lin. 
Semi-globulous ; mouth Columella in a straight 
semi-circular or semi-el- line. 
liptical, closed entirely by 
an operculum ; spire al- 
most effaced. 
a. Natica, (1) Lam. 
Operculum horny. Columella umbilicate. Marine. 
Pl. 9, fig. 24. V. Animal, p. 67. 
6, Nerita, (2) Lam. 
Operculum_ stony, | Columella umbilicate, _ Marine. 
shell thick, Pl. 9, fig. dentated. V. Animal, p, 67. 
e. Neritina, Lam. 
Operculum horny, Columella rarely den- _ Fluviatic. 
at thin, Pl. 9, fig. tated. (3) V. Animal, p. 67. 
(4) In the fossil state, in the London Clay and Crag Marl; at Grignon. 
(2) In the fossil state, at Retheutl, Courtagnon, Houdan, Grignon. 
(3) Those with the columella dentated form the genus Clithon of Montfort, whose 
Clithon corona, pl. 9, fig. 23, differs from the Clithon coronata of Leach. 
