100 LAND AND FRESH-WATER MOLLUSKS. 
GrENus VITRINA. 
The distinctive generic title is derived from 
the Latin word vitrwm, glass. This generic 
group isa connecting link between the Slugs and 
the true Snails or Helices ; for it has the lingual 
dentition and the shield-like mantle of Limaw and 
the globular external shell of Helix. They appear 
to be occasionally animal-feeders, like the slugs, — 
a propensity equally possessed by some of the 
Helices. Vitrina may be readily distinguished 
from Helicella, by the absence of an umbilicus ; 
for all the shells of species of the latter are per- 
forated. The genus is represented in Britain by 
only one species :— 
VITRINA PELLUCIDA—(the Green Glassy Snail) 
(Pl. VI., fig. 43).—The body of this snail is elon- 
gated, too large to allow of the animal retracting 
completely into the shell. The mantle is pro- 
duced into a shield and reflected over the front 
of the shell when the animal crawls, and furnished 
with a tongue-like lobe on the right side; the 
lingual teeth are like those of Limaza, of 100 rows 
of 75 each, and the jaw resembles that of the 
true slugs and cellar snails, in being strongly 
arched from before backwards, produced into a 
beak, smooth or nearly so. 
The beautiful greenish-glassy shell of this 
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