Vol. XI, Nos. 10 & 11.] The Fauna of the Jordan System. 463 
[V.8.} 
cut off from the Jordan valley in much the same manner as that 
of the Dead Sea was permanently cut off from the Erythraean 
valley. 
It is well known that the waters of the Dead Sea met 
their biological doom not by becoming salt but by becoming 
poisonous. As Dr. Christie! has pointed out in a previous 
increase in the specific gravity of the water that took place after 
the outflow disappeared would have killed off a large proportion 
of the fauna, but would not have rendered the lake absolutely 
sterile. The fauna would have been comparable to, even if 
a 
that these fish die in a short time if transferred to De 
Sea water. 
The only way in which I can explain the fact that the 
conspicuous African element in the fauna of such a lake as 
that of Tiberias is practically confined to one group of animals , 
is by the suggestion that conditions have changed to such 
an extent since the connection with the African rivers was cut 
off that most of the Ethiopian forms have perished and that 
those forms which have survived have proved less susceptible 
swamps in the desert east of Damascus—are known to er 
abnormal in their capacity for existence 1n unfavourable 
conditions. oe 
‘Thess fish belong mainly to two families, the Siluridae and 
the Cichlidae—or Chromides as they were formerly . 
The Siluridae are represented by a single species of the 
enus Clarias (C. macracanthus), a genus regarded b — 
ichthyologists as the type of a separate family, the Clariidae. 
