470 Journ. of the Asiat. Soc. of Bengal. [Nov. & Dec., 1915. 
was removed—it has not disappeared in the case of the 
Dead Sea—the salinity of the water decreased owing to the 
resumption of a steady flow and perhaps to climatic changes 
that produced a greater volume in the stream. 
hroughout the foregoing argument it has been assumed 
that the fauna of the Lake of Tiberias is a fair sample of that 
of the Jordan system asa whole. One exception has, however, 
been noted, viz. that of thin-shelled molluscs unable to with- 
stand the chemical action of the water of the lake. With 
this exception, which is not a very important one, the as- 
sumption is justified. The Lake of Tiberias is the only rem- 
nant of the old Jordan Lake in which anything like nor- 
mal lacustrine conditions have persisted, for the Dead Sea 
is of course out of the question, while the waters of Merom 
now form a swamp rather than a lake. They are very shallow, 
endemic in its waters may be partly due to this cause, and 
therefore more apparent than real; but it is also due in part to 
the fact that many animals which would perish in running 
water can live in the still depths of a comparatively deep lake. 
The number of species found in the Jordan and not in the lake 
is small, and may be explained in a similar manner. 
GENERAL CONCLUSIONS. 
My views as to’ the origin of the aquatic fauna of the 
Jordan system may therefore be summarized as follows :— 
!. This fauna is mainly Palaearctic but contains a 
distinct Ethiopian element. 
va e origin of the latter element is best explained 
on the grounds set forth in particular by Gregory 
in his ‘‘Great Rift Valley’’, i 
System. 
3. The peculiar circumstance that the Ethiopian element 
consists exclusively or almost exclusively of fish is 
due to the fact that the particular families to which 
these fish belong possess an extraordinary vitality 
and have very special powers of physiological adap- 
tation to environment. 
4. The absence or paucity of Ethiopian forms among the 
Invertebrates of the system is best explained by 
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