DISTRIBUTION OF LAND AND FRESH WATER MOLLUSCA. IOI 
The broken banding exhibited by specimens of H.. nemoralis 
from Spurn has been noted by Mr. J. W. Taylor,* and is 
attributed to the extreme dryness of the point. The majority 
of those seen in August, 1900, were normally banded; vars. 
hyalozonata, roseolabiata, and albolabiata may be found near 
Ridgmont. 
H. hortensis is uncommon (Railway Bridge, Hedon), and 
I have not met with H. avbustorvum below Hornsea and Rise. 
One specimen of H. vufescens turned up on the Burstwick 
road. H. pulchella, which is noted for its extensive range, 
occurs throughout the district, and Vitvina pellucida is 
practically the only woodland shell in young plantations. | 
II.—FRESH-WATER SHELLS. 
The agricultural drains which traverse the district have 
no doubt contributed to the wide distribution of the com- 
moner fresh-water species, for after heavy rains the water 
rises to the top of their high banks and frequently overflows, 
forniing inland seas, such as are seen at Hollym and Burton 
Carrs, and Lambwath. More dispersion is perhaps effected 
after severe frosts, when the ice from the ditches and marshy 
ground carries with it earth containing aquatic plants and 
shells of every description. In this way, masses of roots, 
two feet square and a foot thick, were brought down the 
Great Ouse after the break-up of the frosts of 1895, and 
stranded on the bank above Lynn. From these, living 
specimens of Bythinia tentaculata, B. Leachit and Limnua trunca- 
tula were obtained, but all the bivalves and Velletia lacustris 
were dead; the reeds subsequently flourished till killed by 
want of moisture, A uniform fauna, however, is not always 
found throughout a given drainage area, or even along a single 
drain. Thus, Nevitina fluviatilis is confined to a short length 
of Sutton drain, the absence of a suitable habitat preventing 
any migration. I have not found it in any other drain in 
Holderness, though it may similarly occur in particular 
lengths. 
* “Monograph of the Land and Fresh-water Mollusca of the British 
Isles,” Vol. I., p. 99. 
+ The following instances refer to other districts, but are worthy of 
record :—Vertigo pygmaa, var. quadvidentata is abundant on the chalk 
approaches of the bridge which carries the Gayton (Norfolk) road over 
the Melton Constable line. The surrounding district is covered with 
sand. H. pomatia, liberated in Forge Valley by Mr. Bean, was alive in 
1868 (C. Ashford, Science Gossip, 1868, p. 160). Mr. Fierke and I 
made an exhaustive investigation in 1894, but did not find it. 
