161 
that both time and changed conditions have affected the fauna and 
brought about the changes that we have observed. Nevertheless in 
studying the fauna and the stratigraphical position of the complex, 
any separation of the two horizons would be unnatural. 
The affinities and age of the fauna. 
The resemblance between the Aral Sea Lower Tertiary Mollusca 
and those of Western Europe (England, Paris, Basin, Belgium, North 
Germany) has been pointed out by nearly all previous writers, espe- 
cially by Trautschold and V. Koenen.!) The considerably enlarged 
number of species described in the palaeontological part of this 
work only support that fact. But there exist some differences. First, 
the number of species peculiar to this fauna is much larger than 
was assumed; secondly, a considerable number of them is more or 
less closely allied but not identical, and the third and most important 
point of difference is the above mentioned assemblage in this fauna 
of the species, which in Western Europe are confined to two quite 
distinct series, viz., to the Eocene and Lover Oligocene.?) In this fact 
apparently lies the explanation of such differences in opinion of pre- 
vious writers regarding the age ofthe fauna. This, however, is nota 
character peculiar to this fauna only, but can be observed very often 
in wast West Asiatic and South Russian regions. Unfortunately we 
know very little about the Lower Tertiary Mollusca of Turkestan 
and Western Siberia, and yet even with those very scarce paleonto- 
logical data we can notice, the above character. Romanovski,“) for 
instance, mentions Ostrea Raincourti, an Eocene form, asso- 
ciated wit O. cyatula and O, ventilabrum, typical Oligocene 
forms of Western and Sout-Western Europe. Karpinski*) gives a 
short list of Mollusca from the Lower Tertiary beds of the eastern 
slopes of te Urall, where Fusus multisulcatus, F. cf. corneus 
are associated with Cyprina cf. planata Sow., and fisches „of 
the Eocene character“. The age of the faunula in the Ferghana 
Series?) has long been discussed because of its somewhat unusual 
assemblage of species, etc. The South Russian Lower Tertiary Mol- 
lusca, being much better known, give us more valuable examples 
of this, in Lower Eocene as vell as in Middle and Upper Eocene 
faunas. 
Pavlov, Nechaev, Arhangelski and other Russian geologists who 
have studied the Palaeocene Molluscan faunas, first proposed a 
) V. Koenen: Unter-Oligocäne Tertiär-Fauna von Aralsee. I. c. p. 4. 
>) See list on p. 
>) Materialien zur Geologie von Turkestan I 1880. 
+) Sediments tertiaires du versant oriental de l’Oural. Bull. Soc. Oura- 
lienne Ekaterinenburg VII (1884). E. Haug cites in his Traite (1908—11) p. 1494 
the following list referring to the above work by Karpinski: Cyprina pero- 
valis, Fusus gracilis, F. multicostatus. I have not been able to trace how 
. these corrections were made. 
°) D. B. Sokolov: On the question of the Ferghana Series (in Russisian) 
Bull. Soc. Imp. Natur. de Moskow 1909 N?* 1, 2, p. 44. 
Idem: Sur les rapports entre l’etage ferghanien et le supracretacč a 
Ferghana. Annuaire Geol. et Miner. de la Russie, vol. XIV, livr. 4—5 (1912) 
pp. 113 & 117. 
Glasnik hrv. prirodoslovnog drustva. 4 
