THE EUROPEAN SEAS. 



211 



had its former expansion has been a climatic one. 

 At present the winter temperature of the northern 

 Caspian falls much below freezing (10°-14° F.) ; 

 even the south Caspian is colder than our English 

 winters. In July the heat of Astrakan is equal to 

 that of Sicily or the south of Spain. During three 

 months the evaporation is very great, and the 

 marginal shallow waters are warmed, whilst on the 

 breaking up of the ice and the melting of the 

 snow the waters rise, and are intensely cold. 

 Such conditions are not very favourable for any 

 large or varied Molluscous fauna, and accordingly 

 we find that it consists mainly of forms which live 

 embedded in mud. 



This Caspian Molluscous fauna is as yet but 

 imperfectly known ; such, at least, is the impression 

 which the assemblage of observed species produces. 

 We miss the Limncece and Paludince which may 

 reasonably be looked for there. 



Rissoa Caspia and two little Paludinelloe {P. 

 variabilis, P. stagnalis) swarm in these waters, and 

 the extent to which their shells must go to increase 

 the sedimentary deposits of the bed of the Caspian 

 is highly illustrative of the conditions under which 

 such thick beds of Paludinella limestone were 

 formed, as may be observed in the tertiary brack- 

 ish-water formations of Maintz and other places. 

 Associated with these are Neritina littumta, a 

 Mytilus, and Dreissena, serving to complete the 

 parallel. 



