373 



The Cambrian Trilobites of Australia and 



Tasmania. 



By R. Etheridge, Jun., Director and Curator cf the 

 Australian Museum, Sydney. 



[Read October 9, 1919.] 



Plates XXXIX. and XL. 



I. Introduction. 



The present communication is an attempt to condense 

 our previous knowledge of the above group of organisms, and 

 to suggest certain changes in nomenclature, as a basis for 

 sounder elaboration by those who may come after and, with 

 access to more complete and extensive material, engage in this 

 interesting study. 



The great drawback to a satisfactory elucidation of our 

 Cambrian Trilobites lies in the imperfection of their remains 

 as presented to us, seldom more than portion of a cephalon 

 or pygidium, oftener simply fragments. Omitting the minute 

 form Agnostus elk edr a crisis, I know of only one instance where 

 the ail-but complete body is preserved, that later described 

 as Ptychoparia alroiensis. 



The terms Lower and Upper Cambrian have been used by 

 some in speaking of the rocks containing these old Crusta- 

 ceans. I have not adopted these divisions in pages that 

 follow, believing we know too little as yet of the Cambrian 

 strata throughout Australia and Tasmania to warrant the use 

 of stratigraphical subdivisions employed either in Europe or 

 America. On the other hand, sufficient facts have already 

 accumulated to justify the use of the term Cambrian simply 

 for a vast thickness of beds, in all probability synchronal 

 with those so termed in other parts of the world ; in this sense 

 it is here used. When it becomes possible to stratigraphic- 

 ally synchronize our oldest fossiliferous deposits, it will be 

 more satisfactory to apply local group names, in other words, 

 a sequence based on local facts and conditions. Two opera- 

 tions will accelerate this, detailed field work and energetic 

 collecting. 



With the view of recording the opinions of others, I have 

 in each instance quoted the horizon assigned to a given species. 



II. History. 



1877. — So far as my researches have progressed, the first 

 geologist to discover Trilobite remains in Australia, afterwards 



