58 
GRAPTOLITES OF AUSTRALIA 
mucros, and the completeness of the thecal overlap. Stage 2 
is characterized by deployment into allied genera. Oncograp- 
tus upsilon and Cardiograptus morsus are the only forms 
that do not seem distinctly paracmic and even these are very 
variable. The stage is marked by tendency towards reduc- 
tion in size with closer thecae, still increasing angle of diver- 
gence leading to biserial forms, variation in mucros, reduc- 
tion of thecal overlap in manubriate forms, grouping of 
thecal origins in sicular region as distinct from concrescence, 
but shown with concrescence in forms like Oncograptus and 
C ardiograptus. Stage 3 is marked by extinction of the group 
except for rare examples. The evidence is insufficient to 
place Maeandrograptus aggcstus and M. tail. The catagene- 
tic varieties of /. caduceus except I. caduceus var. divergens 
are not shown in the table. Thej^ are commonest in Zones Cl 
and D5, and show great variability, making grouping diffi- 
cult. Practically all agree in distally-narrowing stipes. 
He then dealt with Isograptus caduceus and its varieties, 
also with their stratigraphical horizons, with other varietal 
forms, manubriate species, Isograptus forcipiformis and 
Slviagraptus gnomonicus^ Oncograptus and Cardiograptus 
and their development, Maeandrograptus spp. and other 
species. He concluded with remarks on the correlation and 
zonal range of the Isograptidae. 
He defined the new family Isograptidae and gave an 
amended diagnosis of the genus Isograptus. He described 
and figured I. manulriatus, I. Jiastatus sp. nov., I. ovatus. 
He conmiented on the genus Maeandrograptus and described 
and figured M. tau sp. nov. and 31. aggcstus sp. nov. He des- 
cribed Slriagraptus gen. nov. and described and figured 
S. gnomonicus. In conclusion he described and figured 
Didymograptiis eocaduceus sp. nov. and D. hemicyclus sp. 
nov. 
He supplied a page of text figures and a plate. 
R. A. Kehle (128) described the occurrence of graptolites 
and vascular plants on a single slab of shale from the Yarra 
Track, west of Matlock. He identified the graptolite as 
3Ionograj)tus riccartonensis (cf. 139) and the plant as belong- 
ing to the genus Psilophyton. The occurrence of 3Ionograp- 
tus with vascular plants definitely fixes their age as Silurian 
and establishes them as the oldest vascular plants yet 
recorded. 
1934. — W. J. Harris and D. E. Thomas (129) contributed 
a paper on the geological structure of the Lower Ordovician 
rocks of (the County of) Eastern Talbot. 
