66 
PHYLLIYOKA. 
gous to the lateral jaws of Limnea than to the upper 
of the two jaws of Neritina^ and appears to be 
formed of the fusion of these jaws ; for Planorhis 
Cornells has the rudimentary lateral jaws of Lym-- 
nea; in all the other species the jaws are reduced to 
a single strongly arched one^ as if formed by the 
fusion of the three into one. — Moquin Tandorty 33. 
M. Moquin Tandon proposes to characterise the 
genera by the form of the upper jaws. 
In Helix the jaw is lunate^ with three or more 
strong ribs across it, which end in well-marked 
marginal teeth (fig. 25.). 
In Ariony BulimuSy Clausiliay Pupay and Vertigoy 
the front of the jaw is more or less strongly striated 
Fig. 25. 
^ — 
Fig. 26. 
Fig. 27. 
M 
4n\ 
(r 
Jaws of Arion 
Jaw of Limax 
Jaw of Helix 
hortensis., magni- 
gagates, magni- 
pomatia, enlarged. 
fied. 
fied. 
across, and slightly denticulated and crenated on the || 
lower edge (fig. 26.). 
In Limaxy ZoniteSy Vitrinay and Succineay the jaw 
is smooth, without any ribs, strise, or teeth, but has | 
a more or less prominent beak in the middle of its |' 
lower edge (fig. 27.). 1| 
These characters appear to be permanent, as far |i 
as they have been observed, in the more restricted j 
genera, as Vitrinay Succineay Clausiliay Pupay FI?r- 
tigoy LimaXy and Arion ; but there are many ex- 
ceptions even amongst the European species of the 
