454 Proceedings of the Royal Irkli Academy. 



Some of those ^vlio take for granted tliat liuge glaciers OTerran 

 IS^orthem and Central Europe in early Pleistocene times will be more 

 inclined perhaps to favour the view that, if there existed any barrier 

 shutting out the Siberian fauna from Europe, this took the fonn of a 

 glacier. This indeed is the oyjinion expressed by Bogdanov, who in- 

 forms us (9, p. 26) that an immense glacier, covering the greater 

 part of the Ural fountain, prevented the Sibenan fauna from entering 

 Europe, while a northern fauna, including the reindeer, spread from 

 Scandinavia, as far south as the Pyrenees. 



To judge from the mildness of climate in Siberia, duiing the Plio- 

 cene and even during the greater part of the Pleistocene Epoch, it is. 

 extremely unlikely that Bogdanov' s theory could be correct. The 

 barrier, if there was one, must have been of a character not at variance 

 with the teraperate climate, evidently prevailing in Xorthern Asia in 

 Pliocene times. As I mentioned before, there is not only evidence in 

 favour of such a barrier, but also that it was of an aqueous nature. 

 As the existence or non-existence of this barrier plays an important 

 role in the history of the Siberian migration, it is necessary for me to 

 dwell on this subject for some little time before following the final 

 entry of the fauna on European soil. 



Professor Karpinski mentions (47, p. 183) that, during the first half 

 of the post-Tertiary (or Pleistocene) Epoch a large brackish inland sea 

 covered the south-eastern portion of Itussia. This not only included 

 the whole of tlie Caspian and the Sea of Aral, which were counected 

 with one anotlier, but it stretched far to the north of their present boun- 

 daries, as far indeed as the mouth of the Kama, in Xortheru Bussia (see 

 map on opposite page). This vast inland sea communicated probably 

 by a system of lakes and channels, with the Northern Ocean. Professor 

 Karpinski's last assumption is based on the occurrence in the Caspian 

 of some Arctic maiine forms of life, but he does not consider that theii- 

 presence warrants the belief in a direct communication between it and 

 the Arctic Ocean. Unfortunately Professor Sars has not quite com- 

 pleted his investigations into the Crustacean fauna of the Caspian, but 

 what has been known for many years of its general facies, has lead 

 many naturalists to conclude that a direct communication between the 

 inland sea and the ocean must have taken place in comparatively 

 recent times. As Professor Sars in the " Crustacea Caspia " (75 5, p. 

 401) remarks, " The Mysidae are generally regarded as being of true 

 marine origin, and of this family eiglit species are now known from 

 the Caspian, half of which also occur in the Black Sea." Of the Order 

 Cumacea, which is exclusively marine, ten species aie described in 



