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



populated by Mediterranean fauna which penetrated into it after breaking 

 through the Dardanelles. 



Table 148, drawn from the data of A. Derzhavin (1925), F. Mordukhai- 

 Boltovskoy (1939) and M. Bacesko (1940), is a good illustration of this. 



Table 148 



When investigating the fauna of the Dnieper delta, F. Mordukhai-Boltov- 

 skoy (1948) found that on the sands and clayey-sand bottoms of the arms of 

 the delta ' the fauna has on the whole a clearly expressed Caspian character. 

 Fresh-water species are generally of secondary importance, and in the main 

 arms, where there is a bottom of pure sand . . . the predominance of the Cas- 

 pian crustaceans, especially the mysids, becomes even more evident. At some 

 stations Caspian species were found exclusively. ' On rock bottoms the Dreis- 

 sensia biomass may amount to 3-6 kg/m 3 , an amount which has not been 

 found even in the Caspian Sea (see below). On the contrary, in the macro- 

 phyte growths of the littoral zone and in the lakes of the delta typical fresh- 

 water fauna is markedly predominant, while the Caspian elements are either 

 secondary or absent. Subsequently more light has been thrown on this 

 phenomenon through research carried out by Yu. Markovsky (1953-55). 



The fauna of the deltas of the Dnieper and Don are very similar: 

 in both cases ' the significance of the Caspian fauna decreases with a fall in 

 the speed of the current and with the transition to bodies of water of the 

 lake type'. 



Distribution of relicts in the Azov and Caspian basins 



Latterly J. Birstein (1946) and F. Mordukhai-Boltovskoy (1946, 1960) have 



approached from a new standpoint the problem of the time of penetration 



