30 
PROFESSOR P. M. DUNCAN ON THE STRUCTURE 
grow upon the calice of the parent, whose growth they arrest, and thus a superposition 
of generations is induced. In some genera the gemmation is lateral.'’ 
This section of the Madreporaria necessarily included a great number of genera ; and 
as they all could be readily distinguished from those of the other great sections, the new 
arrangement was adopted by palaeontologists. 
It was all the more acceptable because the predominant idea of the geologists of those 
days was favoured by the assertion of the existence of any definite groups of organisms 
which were characteristic of and peculiar to certain geological formations. The Palae- 
ozoic series of rocks was supposed to contain the fossil remains of a fauna and flora 
which became extinct before the deposition of the Triassic sediments took place, and a 
great break in the continuity of life on the earth was believed to have happened. Every 
generalization which appeared to favour such hypotheses was usually accepted as correct 
without being subjected to searching criticism; and consequently the foundation of the 
section Pugosa, in contradistinction to those of the Aporosa and Perforata, was supposed 
to necessitate the inference that the Palseozoic Madreporaria differed most essentially 
from the Neozoic. 
Thus the distinguished author of ‘Siluria’ writes: — “ One of the most important of these 
discoveries, resulting from the labours of Professor Milne-Edwards, and his coadjutor, 
M. Jules Haime, appears to be, that the majority, if not all, of the corals of the Silurian 
system, and indeed of the whole Palaeozoic era, belong to divisions of the coral tribe 
unknown in modern seas : with rare exceptions, these groups became extinct at the close 
of the Palseozoic epoch. If this be established, and the large cup- and star-corals 
(Zoantharia rugosa) and the massive Millepores (Z. tabulata) be, as a whole, distinct 
in structure from the star-corals and Madrepores of the Secondary and Tertiary rocks 
and of existing coral-reefs, we gain a new fact in the history of animal life upon the 
globe, which is in harmony with results obtained by the study of the Crustacea, Mol- 
lusca, and Fish of the older epochs” (‘ Siluria,’ 4th edition, 1867, p. 217). Moreover, 
in a note to page 220 of the same work, the restriction of the non-rugose corals to the 
Mesozoic and Cainozoic periods is inferred. 
Although the Zoantharia tabulata are as numerous in the existing coral-faunas as 
they were in the Palseozoic (and some of the genera are closely allied), the presumed 
fact of the restriction of the Pugosa to the Palseozoic formations tempted many to come 
to the erroneous conclusion respecting the break in the continuity of coral life at the 
end of the Permian age. 
The characteristic nature of the Palseozoic coral-fauna was, moreover, strengthened in 
the minds of some by the able manner in which MM. Milne-Ed wards and Jules Haime 
overthrew the old classification of the corals of the Muschelkalk and St. Cassian strata 
of the Trias, and proved that they were not of Palseozoic genera. Strengthened by the 
opinions of many geologists respecting the limitation of life, a number of able palaeon- 
tologists have persisted in refusing credence to any facts which should prove, if they 
were no longer called anomalies, that the Pugosa were not restricted to the Palseozoic 
