LAND AND FRESH-WATER MOLLUSCA OF PALESTINE. 15 
immense torrents of icy water poured into and chilled the three 
lakes. Still further, the deposits on the sides of the Jordan 
Valley, north of the Sea of Galilee, prove that the influx of water 
must have been so great as to fill up almost the entire trough, and 
thus to form one vast lake upwards of 200 miles in length, and 
2,000 feet deep. There is no evidence, however, that any ocean 
connection was established in the south by the level of the inland 
waters overleaping the high water-shed leading towards the Gulf 
of Akaba. Now this change from a tropical to that of an almost 
sub-arctic climate must have tested severely the endurance of many 
of the molluscan fauna of the Sea of Galilee and its feeders; and 
when we take into consideration also the slight increase of salinity 
in the waters owing to their mixing with the salt Dead Sea, we 
may easily understand how it is that so few of the old marine 
forms have survived to this day. 
But again, when the ice retired, the battle was by no means over. 
Along with the cold had come boreal immigrants, who, with 
characteristic vigour, dispossessed the old molluscan inhabitants 
(especially those of the land), and assumed ownership of all the 
colder districts in the north of Palestine. The struggle has been 
going on ever since; but still, in all the long ages which have 
elapsed since the glacial period, the ancient types, which survived 
so many vicissitudes, have not yet succeeded in re-establishing 
themselves over their lost dominion. We see in these peculiar 
Jordanic molluscs, therefore, simply another beautiful illustration 
of the truth of evolution, and of the derivation of specific forms 
by descent with modification. 
In concluding, I must acknowledge my indebtedness to the 
kindness of Canon Tristram in agreeing so readily to name my 
specimens for me. The total number of molluscan species found 
in Palestine, according to this well-known authority, is 213, of 
which 57 are Palearctic, 8 are Ethiopic, 8 are Indian, and no less 
than 140 are peculiar to the country. 
