Ordoviclaa Rods. 69 



■characteristics uf Oncof/rapfus show its relation to J), cadiiceus, and 

 it seems probable that Oncograptus and Cardiograi>tus, like D. for- 

 cipiformis and ]). caduceus var. manubriatvs, are also late deriva- 

 tives of D. caduceus, and had a very limited range. Here, then, 

 is the life history of TJidymograptus caduceus. Originating when 

 D. hifidus was flourishing in the Wattle Gully stage, oi'' perhaps 

 earlier, it outlived that form, and became fairly conunon in the 

 Middle Castlemaine, as yet showing little if any increase in size. 

 By the time the Victoria Gully stage was reached it had become 

 by far the commonest species, and with favourable conditions 

 reached its zenith in the McKenzie's Hill Ijeds. The conmion fate 

 •of all genera and species now overtook it. It deployed in various 

 directions giving i-ise to O/icor/rapfiis, D. forci2f/fortni-^. Car- 

 ■diograptus, etc. It will be the purpose of the second part of 

 this paper to attempt to show the phylogeny of these and other 

 genera. If the Darriwil beds are placed anywheie l)ut aVxive the 

 Castlemaine beds the development of D. caduceus Ixjcomes unintel- 

 ligible. 



(e) Transitional Beds. 



Victorian graptolite zones are all based on the rise and fall of 

 species. T. fruficosus, D. hifidus, and D. caduceus originated in 

 that order, lived in association, and one by one disappeared, afford- 

 ing a basis for the subdivision of the rocks in which their remains 

 are found. Dr. HalU lias shown how 2\ aj^prorimatus, Nich.. oc- 

 •curring with Lancefield forms at Inglewood and Clarendon, and 

 Avith Bendigo forms at Bendigo and in the Mornington Peninsula, 

 indicates the highest beds of the Lancefield, or the lowest beds of 

 the Bendigo series. 



Now, Oncograjjfus upsilon and Trigonograpfus occur similarly 

 at Castlemaine. At McKenzie's Hill the majority of the forms are 

 so characteristic of the Upper Castlemaine of Dr. Hall that I have 

 'taken them as typical of that zone — more typical even than McCoy's 

 Barker Street beds, where D. caduceus is, on the whole, not so well 

 developed. Yet at McKenzie's Hill Oncograpfus and Trigonograp- 

 tiis are occasionally found, indicating the close proximity of the 

 McKenzie's Hill beds to the Lower Darriwil series. At the Military 

 Rifle Range Oncograptus is also found, though here again it is 

 extremely rare, and the beds are typically Upper Castlemaine. The 

 Rifle Range beds, as shown above, are found to be sxicceeded 

 along their line of strike by Oncograptus beds, which, if one pre- 



1 Recent Advances Vic. Graps., p. 319. 



