pepe ae pats FREER Ea Ra 
DISTRIBUTION OF LAND AND FRESH WATER MOLLUSCA. 103 
shells on recently enclosed land—probably a case of bird dis- 
persion. It is found occasionally inland, but is frequently 
overlooked, as its favourite localities dry up in summer. The 
larger Pl. coyneus inhabits Hornsea Mere, and a ditch in the 
low marshy ground at the head of the Ryehill drain. 
Segmentina nitida, the rarest of the Holderness Planorbes, lives 
amongst the reeds on both sides of Hornsea Mere. The 
gravelly south shore, which is always worth investigation, 
provided me with a dead shell in 1886. Five years afterwards 
I found it living on the north side, and in the following year 
I took it almost opposite on the south. 
A complete collection of the shells of the mere may be 
obtained from the rejectamenta on the south shore, but I 
have never found Limnea glabra washed up there. At Hedon 
L. glabyva shared with Physa hypnorum a short ditch about 
thirty yards long, isolated from all other water. Like other 
glabra localities I have seen, it was dry in summer, though 
the masses of Callitriche, &c., would probably keep the bottom 
damp and favour the growth of the shells, which were larger 
and thicker than any others I have found. On examining the 
place this year I found no signs of Limnaa, Callitriche, or even 
water, while the hoof-marks on the bottom showed clearly 
that the cattle had sheltered from the heat under the high 
bushes which now grow on each side. About a quarter of 
a mile away, in a dry ditch, I unearthed a single specimen 
with the mouth closed by a thin epiphragm, but before I 
reached home it was crawling round the sides of the tube, 
proving that in times of drought—which will occur every 
summer in glabya pools—it follows the example of the planorbes 
and ‘‘aestivates”’ till the autumn rains fill the ditches again. 
These two localities are separated by a drain which runs at a 
lower level, and which was probably cut after their dispersion. 
Mr. C. Hollingworth has recently found L. glabya in abund- 
ance in a third station at Sproatley. It has also been found 
in Inglemire Lane and Haltemprice Lane, near Hull. 
Physa hypnorvium also seems capable of withstanding pro- 
longed drought, for it occurs with L. glabya; in fact, it was 
while watching this species climbing up its thread that I first 
saw the latter. It is not uncommon round Hedon, though 
usually confined to old ditches, and therefore absent from 
Kelsey Hill. 
Mr. C. Reid has noted the occurrence of Limnea truncatula 
in a raised stone cattle trough on the Humber marshes,* the 
water being provided by a deep boring. This may refer to 
the Lincolnshire side. 
* Trans. Norfolk and Norwich Nat. Soc., vol. v. (1892), p. 297. 
