706 
DR W. T. GORDON ON CAMBRIAN ORGANIC REMAINS 
abundance of certain forms in one bed or horizon (especially when the forms are small) 
does not necessarily indicate that the conditions then obtaining were favourable for 
that particular organism. More commonly it indicates quite the reverse, for the 
small size is frequently accompanied by gerontic characters showing that the growth 
was very slow, i.e. that the forms were stunted in their development. 
Since all the specimens were small and relatively complete, the early stages 
of growth were obtained in practically all cases. Thus in particular it was possible 
to test the truth of Bornemann’s idea that Protopharetra is not a genus of the 
Archseocyathinse, but represents a general type of rooting structure, i.e. that various 
genera may terminate downwards in Protopharetra forms. (A direct analogy 
may be seen in the so-called genus of plants — Stigmaria — which has been proved to 
be a general type of rooting structure common to Lepidodendron, Sigillaria, and 
Bothrodendron.) Taylor’s genus Metaldetes certainly lends colour to Bornemann’s 
view, and so also does Spirocyathus, as shown above ; but, in spite of the fact that 
a casual examination might cause one to group the lower parts of the skeletal 
remains with Protopharetra , a closer examination shows that there are differences, 
and that Protopharetra is a distinct genus. 
The biological position of the whole group is still doubtful. The porous skeleton 
suggests affinities with the Porifera, though not necessarily so, since certain of the 
Coelenterata also have porous walls. The non-spicular character of the walls, septa, 
etc., and the thickening of these structures in the lower parts of the cup, favour 
relationships with corals (Anthozoa), while the peculiar internal growths can also be 
paralleled in that group. The points of difference, on the other hand, are too 
conspicuous to allow of any such correlation. Indeed, it is quite as likely that the 
resemblances to sponges and corals are merely superficial and can be explained as 
homoplastic developments. 
Nor can we point to any gradual evolutionary changes within the group itself 
which might give some clue to possible lines of descent. The Archseocyathinse 
appear suddenly as a suite of very diverse forms at the top of the Lower Cambrian 
Series, and on that geological horizon have practically a world-wide distribution. 
True, a supposed organism, Atikolcania, Walcott, from Pre-Cambrian rocks was 
compared with the Archseocyathinse, but the author has since proved that the 
structure was really produced by inorganic means. The whole group, therefore, 
is very isolated and has an extremely short geological range. 
There is certainly abundant evidence that sponges coexisted with these organ- 
isms, but corals are conspicuously absent from rocks of this period. Yet it must 
be borne in mind that many Coelenterata secrete no skeletal elements, so the absence 
of anthozoan skeletons from Lower Cambrian rocks does not necessarily imply that the 
class was not represented in the fauna of that age. The only fossil with any marked 
similarity to the Archseocyathinse is the calcareous sponge Barroisia from Cretaceous 
rocks. Here, however, the skeleton is spicular and its sponge characters undoubted. 
