98 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
if not the only, animal remains in quite considerable thicknesses of the 
deposits. In such cases they may be of value in determining the age 
of the strata, as well as in enabling stratigraphical correlations to be 
made. 
They are valuable also, since their small size enables them to escape 
destruction in the drilling operations which are essential for the adequate 
study of these Tertiary basins, owing to the limited nature and sporadic 
occurrence of outcrops. 
Moreover, although most of the ostracod valves are badly crushed, 
careful examination usually reveals well-preserved individuals with 
distinctive shape and ornamentation, so that more certain specific 
identifications can sometimes be made than is the case with other fossils. 
Another important factor is that some of the species have been found 
to be moderately short-ranged and, with the recognition of charcteristic 
faunal assemblages, the ostracods, accordingly, may be suitable for zonal 
correlation purposes within a basin. It must be admitted, however, that 
some of the simple, smooth-shelled ostracods are definitely long-ranged 
and consequently of little value for purposes of subsurface correlation. 
Owing to their wide geographical distribution, the ostracods have 
also shown themselves to be of value in indicating the stratigraphical 
relations of some of the different Tertiary basins. 
Taxonomic work on some of the ostracods, besides being of value for 
purposes of age determination of the strata, is also helpful in throwing 
light on the environmental conditions of deposition of the sediments. 
For instance, the referring of species found in bituminous shales to 
present-day genera which are known to frequent lake floors, creeping in 
the mud and feeding largely on algal material is suggestive, since this 
is the environment in which bituminous shales are actually formed. The 
presence of these ostracods then can be taken as an index to such 
conditions of deposition. 
Finally, the fact that other Tertiary fossils, apart from the fossil 
fish, are at present of little use for stratigraphical purposes, makes the 
ostracods all the more valuable as fossils. 
Opposed to these advantages there are certain disadvantages that 
limit the satisfactory utilisation of Queensland Tertiary ostracods. 
The minute size of ostracods renders their use in the field 
practically negligible, since accurate identification can only be determined 
with the aid of a microscope. 
Although they may be very abundant, the valves are usually very 
much crushed and broken, and this makes detailed work slow and 
difficult, since a prolonged search is needed to find material suitable for 
identification or accurate taxonomic description. This is particularly the 
case with the Cypridae, the members of which have thin, fragile shells, 
which are seldom met united, as they were only held together by ligaments 
in life. 
The assignment of the various ostracod species to their correct 
genera, also, is often a difficult task. This is due to the fact that the 
genera to which the Queensland Tertiary species are referable were 
originally described by zoologists and not by palaeontologists. The 
classification of recent Ostracoda is based principally on anatomical 
modifications and zoologists, while describing these with great care, have 
