OSTRACODS FROM SOME QUEENSLAND TERTIARY BASINS. 117 
Taxonomic work on The Narrows ostracods and the referring of 
all the species to freshwater genera has also been important, since it 
indicates a lacustrine origin for these Tertiary shales. Furthermore, 
since freshwater fish, unionids, freshwater gastropods, and dicotyledonous 
leaves have also been recorded from this Tertiary basin, it now seems 
clear that the deposit is wholly a freshwater one. 
The study and identification of the various ostracods has provided 
certain information concerning the environmental conditions of deposition 
and origin of these ostracod-bearing shales. The presence and wide 
distribution of species which have been referred to the genera 
Erpetocypris, Ilyodromus and Cypridopsis suggest that the lake was 
shallow but probably of a permanent nature, that its floor was covered in 
part with mud, decayed vegetable matter and algae, and that the 
temperature of the water was probably very close to that found in 
similarly situated lakes today. Ostracods belonging to the genera 
Erpetocypris and Ilyodromus are found today only on the floors of 
shallow lakes and ponds, creeping among the plants, crawling and 
burrowing in the mud, and feeding mainly on algae. Furthermore, 
although Cypris, Cyprinotus and Cypridopsis are swimmers as well as 
creepers, they are known to occur most abundantly in still, shallow 
waters containing a moderate amount of organic material. Accordingly, 
it seems clear that The Narrows ostracod-bearing shales were laid down 
under the above environmental conditions and, since algal and other 
vegetable material was present in varying amounts, it is not surprising 
to find that many of these shales arc somewhat bituminous. Certain 
parts of this Tertiary lake, where the environment was particularly 
favourable, must have teemed with ostracods at the time. It might also 
be mentioned that, from the wide geographical and stratigraphical 
distribution of the ostracods in the basin, it would seem that these 
environmental conditions must have extended over a fairly considerable 
part of the lake, and existed intermittently at least for the time 
necessary for the deposition of several hundred feet of shale. It can be 
concluded, therefore, that the area was slowly subsiding. 
The fact that ostracods are scarce and completely absent from some 
of the shales passed through in boring, however, indicates that the above 
environmental conditions did not extend over the whole lake and 
throughout the entire period of deposition. One other environment, in 
which the amount of vegetable material was so great that the water was 
probably unsuitable for the presence of ostracods, is suggested by their 
absence from most of the higher-grade bituminous shales. Another 
environment, also, in which the amount of vegetable material was very 
small and ostracods were not abundant, is indicated by their scarcity 
in the coarser-grained, non-bituminous shales. Since freshwater 
gastropods have, on the other hand, been found to be more prevalent in 
these coarser-textured shales, they apparently favoured this environment. 
Finally, it must be admitted that the ostracods identified have not 
proved of very great value for the determination of the precise age of 
The Narrows Tertiaries. It is clear, however, that the fauna is fairly 
closely allied to the present-day one, since all the species described have 
been referred to living genera. It is possible, moreover, that some of the 
forms described may even be identical with living, but as yet undescribed 
species, or that some may be very closely related to such forms. Until 
the recent freshwater ostracod fauna of Queensland has been completely 
