CARBONIFEROUS AND PERMO-CAKBONIFEROUS ROCKS, N.S.W. 317 



than seventeen species common to the two, and fonr doubt- 

 fully common. But of these seventeen species four are 

 also recorded from the Productus limestone of the Salt 

 Range (Permian). This leaves thirteen species distinctly 

 of Visean age (Middle Lower Carboniferous) common to 

 the Burindi and Irwin Series. One is therefore confronted 

 with this curious and difficult problem in regard to the 

 Irwin River fauna, viz., that in its relations to the typical 

 Permian and Carboniferous rocks of the Northern Hemi- 

 sphere it is, as tested by the age of the Productus limestone 

 of the Salt Range, distinctly more Permian than Carbon- 

 iferous, but tested by the Australian standard of Permian 

 and Carboniferous (e.g. its relation to the Culm flora and 

 underlying Burindi Marine beds of East Australia) it is 

 distinctly more Carboniferous than Permian. 



Here one must emphasise the extraordinary effectiveness 

 of the Darwin to Adelaide mountainous land barrier which 

 in " Permo-Oarboniferous" or Upper Carboniferous time so 

 completely isolated the West Australian and Northern 

 Territory seas on the one hand from those of Eastern Aus- 

 tralia on the other. Out of about two hundred species 

 recorded in the Permo-Oarboniferous marine fauna of East 

 Australia and Tasmania only the following nine species 

 are at present known to be common to the two : — Nubecu- 

 laria lucifuga var. Stephensi, Fenestella fossula Lonsd., 

 Protoretepora ampla Lonsd., Productus subquadratus 

 Morris, P. undatus Defr., Dielasma cymbceformis MQrris, 

 Aviculopecten Sprenti Johnst., A. teuicollis Dana, Nucu- 

 lana Waterhousei Eth. fll., Agathiceras micromphalum 

 Morris. 



Even in the case of some of the above specie3 such as 

 Aviculopecten tenuicollis, Mr. W. S. Dun considers it 

 doubtful whether some of the above eastern and western 

 forms respectively are specifically identical. An important 



