PHYLLIYORA. 
65 
With reference to the actual size of the teeth^ it 
will be convenient to take the lO^OOOth of an inch 
as the measuring standard ; and therefore the num- 
bers that I shall now use in giving the dimensions 
of the teeth are to be regarded as so many lO^OOOths 
of an inch. 
In Avion ater the central and their neighbouring 
plates are 25 long by 15 wide. In Limax maximus 
they are 20 long by 11^ wide. In Bulimics ob- 
scurus the length of this plate is 7, while the average 
length of all in the row is In Zua luhrica the 
length is and the average breadth 4z\. In 
Clausilia nigricans the length is 4^, and the average 
breadth 3|. The primary lateral plates of Limneus 
stagnalis is 22 long by 12| wide. In Amphipeplea 
glutinosa the corresponding plates are 11|^ long and 
10 wide, which happens to be precisely the size of 
the primary teeth of plates in Planorbis corneus. 
The teeth of Arionidce and Limacidcc are much 
alike, and differ from HelicidcB in having a long pro- 
jecting single apex to the edge teeth. 
The Helicidcc^ on the other hand, show a marked 
disposition to increase the number of apices by bi- 
furcation as they approach the edge. 
Avion atev^ Limax maximus^ and X. cavinatus^ 
I Vitrina pellucida^ Zonites alliavius^ Z, cellarius^ Z. 
\ nitidulus^ and Z. radiatulus have the edge teeth 
I aculeate; Helix fulva^ H, aspera^H, pomatia, Zonites 
I votundatus, &c. have the edge teeth serrate.” — 
j Thompson, 
j The jaw in Limaces and Helices is single, in the 
upper part of the buccal cavity, and is more analo- 
F 
