MR. T. FETCH OK LAND AND FRESH-WATER MOLLUSCA OF NORFOLK. 61 
VII. 
THE LAND AND FRESH-WATER MOLLUSCA 
OF WEST NORFOLK. 
By T. Petcii, B.A. Lond., M.C.S. * 
lira,/ 1 28 th January , 1805. 
In comparison with the list of East Norfolk Mollusca, the following 
one will, no doubt, seem small ; but this might have been expected, 
since there is no district in the West which offers such a happy 
hunting-ground to the conchologist as the Broads do in the East. 
In addition, the spocies named below have been collected within 
easy walking distance of Lynn and Hunstanton, so that the greater 
part remains unexplored. 
The low-lying country to the south of Lynn seems particularly 
favourable for fresh-water forms, but, on closer examination, is 
rather disappointing, as much of the water is brackish, and the 
ditches are, from a naturalist’s point of view, too often cleaned 
out. Consequently, the larger bivalves are rare. I have found 
Anodonta in one locality only. Segment ina nifida occurs at Lynn, 
but will, no doubt, be exterminated by an “improving” Town 
Council. Limncea glabra is found in two small ponds which are 
dry in the summer. 
An interesting point in distribution is brought forward by 
comparing the ditches near the Wash with those on the Yorkshire 
bank of the Humber. In the former, PI. nitidus is the common 
Planorbis, whilst PI. nantileus has not been found ; in the latter, 
the reverse holds, PI. nantileus being present in hundreds in ditches 
and ponds from Hull to Spurn. 
If we accept the theory of dispersion by birds (and both species 
are small enough), ought we not to find the same shell in the two 
localities 1 With regard to distribution by rivers, masses of reed- 
roots, brought down to Lynn by the ice, yielded living specimens 
