66 PHYLLIVOEA. 



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 

 corneus 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 Tandun, 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 

 stronjT ribs across it, which end in well-marked 

 marginal teeth (fig. 25.). 



In Arion, Bulimus, Clausilia, Pupa, and Vertigo, 

 the front of the jaw is more or less strongly striated 



Fig. 25. 



Fig. 26. Fig. 27. 



(0^ 



Jaws of Arion Jaw of Limax 



Jnw of Helir horlensis, magni- gaga les, m&gm- 



pamalia, enlarged. fied. fied. 



across, and slightly denticulated and crenated on the 

 lower edge (fig. 26.). 



In Limax, Zonites, Vitrina, and Succinea, the jaw 

 is smooth, without any ribs, striie, or teeth, but has 

 a more or less prominent beak in the middle of its 

 lower edge (fig. 27.). 



These characters appear to be permanent, as far 

 as they have been observed, in the more restricted 

 genera, as Vitrina, Succiiiea, Clausilia, Pupa, Ver- 

 tigo, Limax, and Arion; but there are many ex- 

 ceptions even amongst the European species of the 



