200 PROCEEDINGS COTTESWOLD CLUB 1903 
Limneza. Five species were found, all of which are 
known as living in the county, the absentees being Z. 
glabra and L. tnvoluta—if the latter be really a species, 
and not a local variety of the polymorphic L. fereger. 
Planorbis. No less than ten species of this genus were 
found,* of which one, P. stremii, is no longer now living 
in the British Isles; whilst two living forms, P. gladber 
and Segmentina nitida were absent. Of these forms the 
most noteworthy is P. s¢ve@mzz, which has only recently 
been detected fossil in these islands.? It was by far 
the most abundant member of its genus at Clifton 
Hampden, there being more examples of this form 
than of all the other species of Planorbzs put together. 
Although it bears a superficial resemblance to P. albus, 
it may easily be distinguished from it by its larger 
size, the constant presence of a keel, and the absence 
of the spiral striz. Mr A. C. Johansen, of the Zoological 
Museum, Copenhagen, who kindly identified the species, 
informs us that it is now living in Siberia, Finland, and 
Northern Scandinavia, whilst it occurred in Denmark solely 
in deposits of the Oak period (Bronze age). Up to the 
present, we have noted it from the dried “Thames 
mud” of the embankment, on the site of the new Scotland 
Yard Gn which it is probably a derived fossil); from the 
Holocene gravels at the same place, and at the Houses 
of Parliament; from Betteridge Road, Fulham; Kew; 
Staines; and the alluvium of the Lea at Walthamstow. 
All of these localities, it will be noted, are in the Thames 
river-system. Here is, indeed, an interesting problem in 
the history of a species. Quite unknown in the Pleisto- 
cene, it is present in great abundance in the later beds, 
while so far as we know it is now quite extinct both 
1 Curiously enough the same ten occur together also in the alluvial deposits of the 
Lea, at Walthamstow. 2 Proc. Malac. Soc. Lond., Vol. iv. (1901), p. 236. 
