BY C. W. DE VIS, M.A. 125 



edging plates " peripheral" to distinguish them from the super- 

 ficial marginals. In the plastron of the tortoises with which we 

 have mostly to deal, the " episternal" is covered by thejugal, 

 part of the interjugal when present, more or less of the humeral, 

 and part of the azygous shield ; the " brachiosternal" plate 

 underlies the rest of the humeral and all the pectoral ; the 

 " merosternal" plate most of the abdominal shield ; the " sacro- 

 sternal" plate the rest of the abdominal and all the ziphisternal 

 shield. The term " neural" is retained for the plates over the 

 line of vertebrae in Trionyx. 



It is hardly necessary to say that although the osteological 

 elements of the test are too important, both in theory and 

 practice, to be confused even nominally with the dermal shields, 

 the value of the latter in determinative work may not be under- 

 rated ; the grooves cut by their edges into the bone beneath are 

 indispensable guides to the zoological position of the source of 

 any fragment under examination. 



The zoologist, with the whole reptile before him, can afibrd 

 to neglect to a great extent indications of specific identity or 

 difference offered by the superficial sculpture of the test. Not 

 so the enquirer who has but bone sherds to examine ; he is com- 

 pelled to have constant recourse to such evidence, frequently to 

 rely upon it alone ; and duly allowing for variability and 

 abrasion, he can generally do so with comfort. 



The writer's thanks are due to Mr. R. Etheridge, Palaeonto- 

 logist to the Mines Department of New South Wales,'-' for an 

 opportunity of examining the chelonian amongst other fossils 

 lately found on the Warburton River and sent to him by the head 

 of the Geological Survey of South Australia, Mr. H. Y. L. Brown, 

 and for permission to figure one of them. 



Fam. TRIONYCID.E. 



Gen. Trionyx. 



Trionyx australiensis, n.s. 



" In some' of the creeks running more to the south-eastward 

 from the Peak Downs, and like Theresa Creek, belonging to the 

 Mackenzie River system (<"..'/., Crinum Creek) occur bones of 

 Trionyx and Crocodile. A year or two ago I forwarded some of 

 these to my friend, Professor Huxley, whose determination I 



' Now Acting Curator to the Australian Museum, Sydney. 



