314 
GLACIAL SURVIVALS. 
FRANK ELGEE, 
Middlesbrough. 
(Continued from page 276). 
As the unglaciated area of North East Yorkshire comprises 
the deep, large sheltered valleys lying to the south of the 
anticline (Rosedale, Farndale, etc.,) their natural history must 
be particularly interesting. Unfortunately, however, very few 
records therefrom are known. The evidence, however, that 
many kinds of widely distributed Land and Fresh-water 
Molluscs lived in them throughout the Ice Age is decidedly 
strong. There is direct evidence that many of the most 
abundant freshwater shells can withstand a very severe 
climate, and would therefore be capable of surviving the 
Ice Age. 
One of these is Physa hvpnorum, the shell of which is so fragile 
as to need most careful handling. It has been noticed on the 
peninsula of Taimyr in North Siberia in 73° 30’ N. lat., where 
the mean annual temperature is below 10° F. with a range of 
from 4o° F. in July to — 30° F. in January.* If a species so 
delicate can exist under a frost of 62° it ought to have been 
able to survive on our driftless area. 
Again, those common Pond Snails Zizmncea stagnalis, L. 
peregra, and L. truncatula, as well as Planorbis albus, live at 
the present day in Greenland, whilst Zémnca auritcularia has 
been known to survive after having been subjected to a frost of 
34°. Paludina vivipara and Anodonta anatina have resisted a 
temperature of 23° F., and the former produced young shortly 
after being thawed out of ice. + In fact, most of the British 
land mollusca, except the operculate species, are extremely 
hardy, and may therefore have existed in the large sheltered 
dales throughout the Ice Age. 
In confirmation of this glacial survival of Mollusca, the 
Arctic Freshwater Bed of the Norfolk coast contains, associated 
with typical Arctic plants such as the Dwarf Birch and Willow, 
Succinea putris, S. oblonga, and Pupa muscorum, and the wing 
cases of beetles. | Altogether at the present time 4o species of 
terrestrial and freshwater molluscs inhabit circumpolar regions ; 
* Cam. Nat. Hist., Vol. 3, p. 24. 
it Opes Gay [Oks 
t Geikie, ‘Text Book of Geology,’ Vol. II. 
Naturalist, - 
