INTRODUCTION. XXlll 
set, and it remains for some zealous conchologist to add a 
fourth, Hygromia revelata, which should be looked for on hills 
near the coast in the extreme west of the county. 
With the single exception of Geomalacus maculosus, all the 
Lusitanian species occur in the Channel Islands. 
The Census List published by the Conchological Society 
forms the basis of the list given above, which shews the com- 
parative distribution of the land and freshwater mollusca of 
the five south-western counties of England. Records marked 
X have been verified by the Society’s Recorder. Excepting 
Dorset, all the counties are divided into “ vice-counties,” the 
areas of which are defined as follows in the Census List. 
Cornwall W. and E., divided by the high road from Truro 
through St. Columb to the inland extremity of Padstow 
Creek. 
Devon N. and §., divided by the watershed line which com- 
mences at the Tamar, about midway between Tavistock and 
Launceston, passes over the ridge of Dartmoor, and joins the 
western canal at Tiverton. 
Somerset N. and S., divided by the river Parret from 
Bridgwater to Ilchester, the line thence curving round to the 
north extremity of Dorsetshire. 
Wilts N. and S., separated by the Kennett and Avon Canal. 
I do not quite understand what is implied by the above 
definition of the dividing line of the vice-counties of Somerset, 
which is apparently based upon H. C. Watson’s subdivision in 
Cybele Britannica, and prefer to divide north from south 
by the Parret to Langport, and its tributary the Yeo to 
Ilchester and Yeovil. The Parret does not pass through 
IIchester. 
One hundred and thirty non-marine species have been re- 
corded from the five counties. Hight are not known to occur 
in Somerset, viz., Hygromia revelata, Férussac; Hygromia 
montivaga, Westerlund; Helix pomatia, Linné; Helix pisana, 
Muller; Vertigo substriata, Jeffreys; Vertigo moulinsiana, 
