Vol.51.] FRESHWATER LAMELLIBRANCHIATA. 339 



P. subcastor, and P. oJcensis — are known in Russia from the upper 

 horizons (A, B, C) of the Permian marls and sandstones of the 

 Oka- Volga basin. 1 These upper horizons, according to the facts ex- 

 plained in my above-quoted paper, 2 I determine as the freshwater 

 equivalent of the German Zechstein. Consequently, the Beaufort 

 Beds of the Karoo Series, if considered as a homotaxial equivalent 

 of those deposits, ought to be regarded as Upper Permian. But it 

 is necessary to remark here that, with regard to the age of these 

 rocks, Russian geologists cannot come to any fixed conclusion. The 

 majority refer them to the Upper Permian, and only a few regard 

 them as passage-beds between Permian and Trias. From what I 

 have said above it is evident that the lamellibranchiata of the 

 Upper Permian marls and sandstones of Russia resemble those 

 from the Beaufort Beds of South and Central Africa. The Permian 

 freshwater lamellibranchiata of Russia, which bear traces of genetic 

 relationship with the Carboniferous Anthracosidae, and were already 

 well represented in Permo-Carboniferous and Lower Permian 

 times, are undoubtedly much older than the African fauna of the 

 Beaufort Beds ; this, we may conclude, emigrated from Russia. It 

 is probable that the Gondwaua Beds of India have been the con- 

 necting-link between these deposits. But even if we admit, during 

 the Permian epoch, the existence of an uninterrupted Russian- 

 Indo- African Continent, the similarity of the freshwater fauna of 

 such distant localities as Eastern Russia and South and Central 

 Africa will still remain one of the most interesting problems of 

 geology. The flora and even the rich vertebrate fauna from these 

 Russian Upper Permian deposits, which I consider as homotaxial 

 and synchronous with the Beaufort Beds of the Karoo Series, have 

 not yet been described. The numerous remains of reptiles found in 

 these deposits will probably prove, after a close study, to have a 

 greater resemblance to the African Theriodontia than the new group 

 of Deuterosauria, created by Prof. H. G. Seeley, which includes 

 forms from the lower horizons of the Russian Permian formation. 



Description op Fossils. 



During my residence in London I have been enabled to study 

 the following collections from the Karoo Series of South and 

 Central Africa : — 



1. Those in the Museum of the Geological Society of London, 

 made by Mr. Bain and Dr. Rubidge, some of which specimens 

 required development before I could ascertain their characters. 



A. Localities. South Africa, Karoo Desert and its vicinity, and Graaf 

 Reinet. A reddish-brown sandstone with fossils, amongst which the 

 following are described by Daniel Sharpe : Iridina (?) rhomboidalis, 



1 Last year Netshayeff found some species of the above-mentioned groups in 

 marls and sandstones of Eastern Russia, but I regret that I am unable to 

 agree with most of his definitions, Trans. Nat. Hist. Soc. Kasan, vol. xxvii. 

 (1894) p. 4. 



2 Palaeontographica, vol. xxxix. p. 210. 



