ANALYSIS OF ANCIENT AND PRESENT CASPIAN SHELLS. 
307 
In seeing the wide extension of the most common species of the fossil shells 
enumerated in the preceding table, no one can fail to be convinced, that whether 
imbedded in the rocks forming the shores of the Black, Azof or Caspian seas, they 
once all lived under the same waters. Throughout all that sea of ancient times, 
certain peculiar forms of the genus Cardium 1 constitute the characteristic feature of 
the fossils, and also, it will be observed, of the present Caspian. In fact, of the 
fifteen species enumerated by Eichwald 2 , seven are still living exclusively in the 
Caspian, two in the Black Sea, two are common to both seas, and eight are fossil ; 
whilst of these last eight species, four are identical with living forms, and four seem 
to be lost. But even the species presumed to be lost are so closely allied to those 
now inhabiting the Caspian, that we cannot avoid recognising in them the same 
peculiar Aralo-Caspian type, unknown in all other regions of the globe. It is 
worthy of remark, that one species, the Adacna color ata (Eichw.), which has been 
found living in the rivers Volga and Don, as well as in the gulf of Nikolaieff and 
the Palus Mceotis, offers a good analogy to explain the habits of the Cardiacese of 
the steppe limestone. It is further remarkable, that the Adacna plicata, which 
Eichwald cites from the gulf of Asterabad in the Caspian Sea, has been found by 
us living in the freshwater lake Akerman®, near Odessa, and within forty to fifty 
versts above the mouth of the Dniester. This fact, added to those cited by Eich- 
wald, of the coexistence of numerous Paludinm with C'ardiaceae, and analogous to 
those inhabiting the present Caspian, would lead us to believe, from zoological 
data alone, that the Caspian of our day is simply the residue of the great Aralo- 
Caspian Sea, whose fauna was so dissimilar from the oceanic deposits of the aera 
in which it was accumulated. 
But notwithstanding all previous researches, our knowledge, it must be allowed, 
is yet too limited to enable us to reason very closely upon the relative change in 
the inhabitants of the former and present Caspian. In the lists of M. Eichwald 
we see, indeed, that several species are now living which have not been found fossil, 
1 Deshaycs retains entire the genus Cardium for all these forms, hut Eichwald forms for them the genera 
Adacna, Monodacna, and Didacna. 
9 The work of M. Eichwald here cited must he considered as the verification and support of many of 
the opinions contained in his former volume, Alte Geographie des Kaspisclien Meeres, des Kaukasus und 
des Siidlicken Russlands. Berlin, 1838. 
s i n the same lake we found the Cardium. pseudo- Cardium (Desh.), (Mem. Soc. Geol. de France, 
vol. iii. pi. I. f. l and 2.), which by a total absence of lateral teeth and other characters is very nearly 
allied to the Cardiaceae of the Caspian. 
