360 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



had a salinity similar to that of the present Caspian Sea. Their population, 

 consisting of numerous species of Didacna, Adacna, Dreissensia, Neritina 

 and Micromelania, was close to the present-day Caspian fauna. I. Gerasimov 

 and K. Markov (1939) suppose that 'as a result of the loss of salinity of the 

 Apsheron basin immigrants from the west, from the Black Sea (Kuyal'nik- 

 Chauda) appeared in it. In the Baku basin era the flow of immigrants (from 

 Chauda) had evidently increased still further. Forms of the Pontic fauna 



Fig. 177. Chaudinsk and Apsheron basins (Archangelsky 

 and Kolesnikov). 



which had evolved in the Black Sea began to immigrate into the Caspian 

 Sea.' 



The closed brackish Apsheron lake-sea obtained its fauna from three 

 sources: (7) from Akchagyl (Clessinia, Apscheronia), (2) from some fresh- 

 water source (Neritina, Melania, Melanopsis), and (3) in great quantity from 

 the Euxine region of the Chauda basin, probably through its connection along 

 the Manych depression (Dreissensia, Didacna, Monodacna). The modern 

 Caspian fauna is the result of a further, but now independent, evolution of 

 this fauna in the basin of the Caspian Sea. 



History of the Tertiary fauna of the Caspian Sea 



Reviewing the history of the Caspian Sea fauna during the Tertiary period, 

 V. Bogachev (1932) lays stress on the numerous marked changes of fauna, 

 which seem to break the genetic link of the fauna of one era with that of the 

 subsequent one. He discerns such interruptions in the transition from the Sar- 

 matian fauna to the Maeotic, from the latter to the Pontic, and from the Pontic 

 to the Akchagyl. Bogachev explains these changes by assuming, in accordance 

 with the views of E. Suess (1888), the existence of 'refuge' bodies of water 

 (' caspians ' as Suess called them) in which one or other fauna could survive 



