BY W, S. DUN, W. H. RANDS, AND PROFESSOR DAVID. 305 



Mr. R. Etlieridge, juiir., adds a footnote to the effect that in a 

 collection from the Lake Eyre Basin, submitted to him by Prof. 

 R. Tate, an exactly similar matrix and mode of preservation of 

 the fossils exists. 



A sketch section is attached showing the position of the lime- 

 stone (Plate xvii.). 



iii. — Description of the Forms figured. 



In a preliminary note like the present we have selected for 

 figuring two forms which we believe to be Diatoms, one example 

 of the Radiolaria, and one which we believe to be an Infusorian 

 type, allied to, if not identical with, Tintinnus. 



Nearly all the micro-organisms are preserved in the form of jet 

 black material, with the exception of the Diatom (PL xviii., fig. 2). 

 The latter is most frequently represented by a cast in clear calcite, 

 but in several cases a black network can be seen enveloping the 

 calcite. 



As regards their mineral constitution, on treatment in dilute 

 acetic acid it is found that the greater part of the netted forms 

 disappear completely. Those which are left intact are mostly 

 Coscinodiscus, or some allied type of Diatom. So far as our 

 experiments went, no Radiolarian shells were noticed among the 

 residues after treatment with acetic acid, which suggests either 

 that the skeletons visible in the thin sections of the Maranoa 

 limestones have been replaced by calcite, or that the skeleton was 

 originally acanthinous. The fact that most of the black nets 

 disappear after treatment with acetic acid, considered in con- 

 junction with their shape and size, suggests that they are 

 Infusorian loricae, and that these organisms outnumbered the 

 Diatoms and Radiolaria in the Maranoa limestones. 



{a) Diatoms. — The form referred by us to the genus Coscino- 

 discus (PI. xviii., fig. 1.) is disc-shaped and circular in outline. 



Its diameter is 0-095mm.,and the diameter of the meshes varies 

 from 0001 25 mm. to 0001 7 mm. The disc is slightly convex, 

 the amount of departure from a plane surface at the centre of 

 the disc being about from 0*0004 to 0*0005 mm. The openings 



