1886. } Zoology. 387 
possessor of luminosity, if otherwise palatable, does not seem to 
escape capture. An examination of the stomachs of fishes makes 
this clear, except, perhaps, in the case of the herring, which, 
however, is chiefly a surface fish. Further, it is not evident that 
such animals are luminous at all times, for it is only under stimu- 
lation that many exhibit the phenomenon. 
Tue Fauna oF THE ARALO-CASPIAN Basin.—There is ample 
evidence that the waters here had formerly a much wider exten- 
sion, but the exact time, or times, when this occurred—although 
geologically recent—has yet to be determined. Dr. S. P. Wood- 
ward, in his Manual of the Mollusca, says the Aralo-caspian 
limestone indicates the former presence of a great inland sea— 
larger than the Mediterranean—at a time previous to that of the 
Mammoth and the Siberian rhinoceros. This steppe-limestone 
rises to a level of 200 or 300 feet above the present level of the 
aspian. 
The fact of the waters of the Caspian and Aral being only 
brackish, and by no means very salt, leads me to think that 
the basin has not been a close one for a very long period. 
General von Helmersen found well-preserved specimens of two 
kinds of shells, viz., Cardium edule and Dreissena polymorpha, in 
the sands of the desert of Harakum. Both these species still live 
in the Caspian. And Helmersen expresses his belief that the 
entire country from the Aral on to the sandy deserts of Akkum 
iS an old sea-bottom (Quart. Journ. Geol. Soc., 1869, Vol. xxv, 
Memoirs, p. 8). ie ; 
The present surface of the Caspian is eighty-four feet below 
that of the Black sea, and according to Major Wood, a rise 
of 220 feet would cause the waters of the Caspian to overflow the 
watershed of the Tobolsk, a tributary of the Obi. 
According to the same authority, a rise of twenty-three feet in 
the waters of the Black sea would cause it to overflow into the 
an by the line of the Manytseh. 
From these figures it appears that if the level of the Caspian 
Were to rise (84 X 23) 107 feet, its waters would find their way — 
Westward into the Black sea, and if the outlet in that direction 
Were blocked so as to permit the surface of the Caspian to rise 
220 feet, the waters would escape northward into the Tobolsk and, 
down the valley of the Obi into the Arctic ocean. Now the Cas- 
: <, Salmon, some of which are species that go up rivers from the sea. 
