156 Barber,— The Structure of P achy theca, //. 
In the best parts (Fig. 9), the cells end at a short 
distance from the periphery, and are bounded externally by 
a clear yellow layer comparable, in appearance, with the 
mucilaginous layer bounding many existing Algae. 
The branching occurs near the extremity of the filaments, 
and is common — as many as ten distinct branchings appearing 
in one-fifth of the circumference. There appears to be a 
frequent tendency towards anastomosis of the ends of the 
filaments, but this appearance is probably due to the con- 
ditions of fossilisation. The ends of the filaments are fre- 
quently dilated (Fig. 9), although this may be due to in- 
cipient branching. It seems to me possible that this swelling 
or branching has some connection with the reproduction of 
the plant. 
Slide 11 (Fig. 10) contains a beautifully cut section in the 
same condition as 1, 2, and 3. There is, however, no zone of 
oval bodies : that is to say, the spaces separating the radiating 
filaments do not swell at their medullary ends. This is a 
matter . of importance, as explaining the absence of oval 
bodies from a number of specimens where we might expect 
to find them. Thus in all the specimens from the Transition 
Beds (Figs. B 9—1 1), it was noted that the inner ends of the 
radiating black lines were not swollen. This difference from 
Sir Joseph Hooker’s specimens was of so marked a nature, 
that I hazarded the suggestion that the organisms were 
possibly belonging to different species. But the present 
specimen, by the absence of a distinct zone of oval bodies, 
renders the subdivision of the genus Pachytheca at present 
superfluous. 
There are certain other slides of Pachytheca which do not 
admit of such a ready explanation ; although the present 
conclusions, founded upon the examination of something like 
forty slides and specimens, are in no way affected by these 
unexplained cases. One of these specimens, on Slide 12, has a 
curious star-like body in its centre much resembling a youthful 
Rivularia, This may have arisen in the following way. 
A disturbance in the regularity of the radiating processes 
