12 
PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
Typical Cretaceous gymnosperms, like Nathorstia, are spasmodi- 
cally present in the Queensland floras. In the very far north, at 
Pluto ville (see Walkom 1928), they are abundant in pre-Aptian beds 
but are rare in the south. They are not present in the Aptian flora of 
the Maryborough Series and are very sparingly present in the post- 
Aptian Burrum Series. Some of the typical, abundant plants of the 
Northern Hemisphere, notably the Cycadeoidea, did not reach Australia. 
This suggests that the early Mesozoic-type flora ( Thinnfeldia Flora) 
evolved in the Permian of Gondwanaland and spread late in the Triassic 
to Europe; while in contrast the later (Cretaceous) gymnosperm flora 
arose in the northern regions and spread south. 
Generally, in the Lower Cretaceous floras of the southern areas 
of Queensland, gymnosperms of types that dominated the Jurassic are 
still overwhelmingly the dominant forms. Thus, if the Stanwell Series, 
on the evidence of the mollusca, is very early Cretaceous, it is not 
altogether surprising that all the forms so far found are of the early 
gymnosperm types. 
DESCRIPTION OF SPECIES. 
(From material in the collections of the Geological Survey of 
Queensland.) 
Genus Iotrigonia van Hoepen 1929B. 
(Genotype by original designation: Iotrigonia crassitesta van 
Hoepen, p. 7, pi. II, figs. 4, 5; pi. Ill, figs. 1, 2. Lower Cretaceous 
Ndabana beds, Umsinene River, Zululand.) 
Trigonias with V-shaped ribbing on the disc have appeared on 
several occasions. A middle Jurassic group was separated as Vaugonia 
by Crickmay in 1932 (Type: V. veronica Crickmay), and another 
of Lower Cretaceous age was named Iotrigonia by van Hoepen in 1929. 
No other groups have been given generic recognition. These two are 
but partial homoeomorphs, ornament on disc and area differing 
considerably in the two groups." ^V-shaped ribbing arises in each 
group by a marked angularity developing between the anterior and 
posterior parts of the ribbing on the disc in the late nepionic or neanic 
stage, and this becomes exaggerated quickly into an acute angle forming 
a V. It may be regarded as the limiting stage of a tendency which in 
other groups of Trigonias (e.g., Trigonia diversicostata Whiteaves, 1876, 
p. 68, pi. X, fig. 1) is halted when the angularity does not exceed a right 
angle. In Iotrigonia the tendency is more developed than in Vaugonia, 
the angularity of the ribs being markedly more acute, reaching its 
acme in 7. limatula. It may even be, as Ivitchin has suggested in 
dealing with 7. van and 7. v-scripta , that the genus is not strictly 
monophyletic. 
Dietrich (1933, p. 33) has dealt briefly with the similarities of 
the two genera, and Rennie (1936, p. 338) has discussed at length the 
genus Iotrigonia. Reference should be made to two papers by Kitchin 
(1903, p. 70 and 1908, p. 110) written long before the generic name 
was given, in which the relationships and affinities of the group of 
species now separated as Iotrigonia were discussed in admirable detail. 
