a, 
DISTRIBUTION OF LAND AND FRESH WATER MOLLUSCA. 99 
we should expect to find them all along from Hull to Spurn. 
Transportation on drift-wood from some point higher up the 
river seems the most probable explanation, especially as they 
occur in a bend of the bank into which they would naturally 
be swept by the current. 
The same theory accounts for the occurrence at Spurn of 
such unexpected species as Pupa marginata, P. umbiltcata, 
Vertigo minutissima (found under an old basket), Helix pygmea, 
Zonites fulvus; and it is rather remarkable that all these are 
found in the highest part of the bend where flotsam of every 
description is cast up by the tide. Pupa marginata is more 
numerous at Paull Holme than at Spurn, though this can 
hardly be taken as confirmatory evidence. The genus Pupa 
holds the record for dispersion: ‘‘It inhabits all the six 
zoological regions, and has been found in the Palzozoic coal 
measures of Nova Scotia.”* Other Holderness localities 
for P. umbilicata are Patrington; a bank near the cliff, north 
of Withernsea; and Burstwick. In the last-named locality 
one specimen was found on a fallen elm. 
As Helix virgata is the chief sea-coast Helix, it is not 
surprising that the variety nigrescens occurs at Spurn; but it 
should be noted that the only other colony is on chalk (Isle 
of Wight), and that near Kilnsea it is found with the aliens 
mentioned above. I saw three specimens in 1895. 
I have only one Holderness record of Buliminus obscurus— 
an empty shell, retaining its original colour, found amongst a 
group of trees near Welwick. After careful search we failed 
to find any others, though, as the trees were old, it could not 
have been a solitary specimen introduced with them. 
Bale Wood, Aldborough, furnishes Helix aculeata and Vertigo 
edentula ; both are fairly numerous, and were probably intro- 
duced with the trees. V. edentula is also found, with Helix 
pygmea, in the woods on the north side of Hornsea Mere. 
Here, again, we have recent plantations. 
Vertigos are the joy—and despair—of every conchologist, 
and I have spent days in searching for them in various parts 
of the district, but my only other records are V. substriata, in 
rejectamenta on the banks of Hedon drain, and V. antivertigo, 
which is common amongst the wet moss between the trees 
and the reeds on the north side of Hornsea Mere. It is best 
taken by placing bulrush stems on the moss after the herbage 
has been mown, and examining them every day. Would that 
all vertigos were found as easily!  Zownites mitidus, another 
* Kew, ‘‘ Dispersal of Shells,” 1893, p. 115. 
