186 i C. F. LASERON. 
none were actually visible on these processes, though occas- 
ionally they seem to encroach upon their borders. This is 
probably due, however, to the state of preservation, as 
Mr.W.S. Dun, Government Palezontologist, informs me that 
cells always occur on the cross-bars of the type P. ampla 
from Tasmania. In Polypora, the smooth or faintly striated 
cross-bars are absolutely devoid of cells. This is well 
shown on Plate VIII, fig. 2. 
But the character which is probably most important, yet. 
which appears to have been largely overlooked, is that in 
Polypora, the cells themselves are more or less oval in 
section, separated by thicker walls, and they are arranged 
in definite longitudinal lines or ranges, and not diagonally 
as in Protoretepora; also there is an absence of the rhom- 
boidal ridging upon the surface of the cell-bearing layer. 
McCoy in his original description says, referring to the 
cell apertures, that the margin of these is never raised, 
but though this might apply to his type species, P. den- 
droides, it hardly applies to other species of the genus. 
At this stage, it seems as if the differences between 
Polypora and Protoretepora were well defined, but a con- 
sideration of American and Indian species again involves 
the whole question in doubt. 
In the first place, many of the Indian Carboniferous. 
species, well described and figured by Waagen and Pichl, 
would on Australian evidence be referable to Protoretepora,. 
for the rhomboidal ridging, dividing the cell mouths on the 
surface of the colony is occasionally very prominent, and . 
the form of the colony is undoubtedly cup-shaped. 
But a study of American species still further increases 
the difficulty. The Paleeozoic beds of the eastern United 
States are probably the least disturbed, and contain a richer 
and better preserved fauna than those of any other part of 
the world, ranging from the Lower Silurian to the Car- 
