PRESENT HISTORY AND DISTRIBUTION 59 
and Pisidium, Plate XV., Fig. 6) climb about in the 
weed. Freshwater Mollusca are also not infrequently 
found living in water-pipes and cisterns connected 
with artificial supply. 
Altitude has no terrors for the freshwater Mol- 
lusca, Limnea Hookeri having been taken at a height 
of 18,000 feet above the sea. On the other hand, 
at a depth of 180 fathoms in Lake Baikal, some 
Paludestrinide peculiar to those waters have been 
met with, The most northern occurrence of a 
freshwater Snail is that of Apflecta hypnorum (a 
British species) which in Siberia attains as far north 
as 73° 30’ in the Taimyr Peninsula. 
Just as the marine Mollusca break their bounds, 
so will the freshwater pass theirs, and essay to 
trespass on the land. The Limneide commonly 
crawl on the wet banks out of the water and in 
moist spots where swamp-loving terrestrial Pul- . 
monates, like the Amber-Snails (Succinea, Plate XIII., 
Fig. 14), etc., love to pass their existence. 
Among marine forms found on land may be named 
a remarkable Periwinkle, Cremnoconchus, which occurs 
only on wet cliffs in the Ghats of Southern India, 
thirty to fifty miles from the sea. Another Peri- 
winkle, Littorina arboricola, lives on trees fully 100 
yards from the backwaters of Trincomalee Harbour, 
and is never known to enter or be covered by the 
water. The Rhipodoglossate, Neritodryas, a relative 
of Theodoxis, occurs on trees of some height in the 
