164 
Natica (Naticina) labelata Lam. 
Natica (Naticina) obovata Sow. 
Calyptrea striatella Nyst. 
Dientomochilus (Echinochilus) planus Beyr. 
Cassidaria nodosa Sol. 
Eutritonium (Sassia) cf. flandricum de Koninck. 
Semifusus (Mayeria) errans Sol. 
Admete (Bonellitia) evulsa Sol. 
Admete (Bonellitia) laeviuscula Sow., etc. 
Now the question arises whether this fauna is of the Eocene 
or of the Lower Oligocene age, in other words, whether the Mol- 
luscan fauna here preserved its Eocene character during the Oligo- 
cene period, or whether the Oligocene species had already appeared 
in the Eocene. The following reasons, in addition to the above 
cited observation of N. Sokolov, seem to place its Eocene age be- 
yond doubt: a) Nowhere in West Siberia and Turkestan has the 
existence of a marine Lower Oligocene fauna been palaeontologi- 
cally proved. b) The appearence of the Oligocene species in the 
Middle and Upper Eocene beds of Western Asia as well as of 
South Russia. Also the fact that some species which in Western 
and South-Western Europe are equally common in the Eocene and 
Lower Oligocene, are found almost exclusively in the Eocene beds 
of these and adjacent regions.!) c) The most common remains of 
Vertebrates in the Aral Sea Tertiary beds are the teeth of Odonta- 
spis elegans Agass. and O. macrota Agass. (Mr. Bateson’s Colle- 
ction, Sedgwick Museum, Cambridge), two species very common all 
through the Eocene of the Anglo-Paris Basin. Also the only two 
species of Briozoa, that I haveseen represented both in the Lower 
and Upper horizon of the Aral Sea Tertiary, are identical wit 
Lunulites radiolatus Lam. and L. urceoplatus Lam., from 
the Bracklesaam beds in England. 
It is much more difficult however to determine more precisely 
the age of the fauna, not only because of the unusual assemblage 
of the species, and the other above mentioned characters of the 
fauna, but especially because of the difficulty of knowing what value 
to give as guides in correlation to the allied forms, which in this 
case represent the majority of the species. For this reason it will 
be necessary to make a more detailed analysis of all the facts, that 
can be taken into account for this purpose. 
The most valuable results can be obtained by a comparison 
of this fauna with those of the Budzak,?) Kiev?) and Harkov Series 
of South Russia. The resemblance between them is considerable. It 
Pa 
“”»oO0o000000 
') For instance: Pecten Biarritzensis, P. Thorenti, Spondylus Buchi, S. ra- 
dula, Cardita Laurae, Ostrea Martensi, Pycnodonta Brognarti etc. 
') See: v Koenen: Uber die Tertiarversteinerungen von Kiev, Budzak 
und Traktemirov. Zeitschr. d. D. geol. Gesell. XXI (1869) S. 587. N. Sokolov: 
Die Untertertiaren Ablagerungen Südrusslands. Mem. Com. Geol. St. Petersb. 
IX, 2, (1893). 
Idem: Guide des excursions du VII Congrčs Geol. Internat. XXI. Excur- 
sion au Sud de la Russie p. 9 (1866). 
%) Fuchs: Die Conchilienfauna. Verh. d. k. Russ. Miner. Gesell. 2te. Ser. V 
p. 66 (1369). 
