210 R. F. Tomes—On Heterastrea, Lower Lias. 
wall by which the calice acquires the appearance as if a double wall 
were present, as in the Paleozoic genus Acervularia. By degrees 
the margin extends itself, until it blends with the thick surrounding 
margin of the older calice. Laube’s figure illustrates the process 
above described. But both description and figures will apply with 
greater accuracy to rejuvenescence than to calicinal budding, which 
process in Acervularia, to which that of H'lysastrea has been likened 
by Laube, is a process of multiplication, and in neither his description 
nor in the figure is there the slightest indication of an increase in 
the number of the corallites by calicinal budding. On the contrary, 
there are many small calices appearing amongst the larger ones, just 
as they would appear were they the result of marginal instead of 
calicinal gemmation. 
Prof. Duncan, in describing the South Wales Elysastree, says that 
the budding is extracalicular, but that the bud probably has its 
origin in the centre of a corallite. No evidence is however adduced 
in favour of the latter supposition. None of my specimens from the 
Sutton Stone exhibit the budding process as it is shown in Prof. 
Duncan’s figures, i.e. between the corallites; but they have rejuve- 
nescence just as in Laube’s figure. The young calices between the 
old ones in Prof. Duncan’s figures are just such as would proceed 
from marginal gemmation in a genus in which the corallites are 
imperfectly united by their walls, and I have little doubt but that 
gemmation in Hlysastrea is marginal, as it is in the so-called Liassic 
Isastree. 
The nature of the endotheca in the South Wales Elysastree is 
very apparent and closely resembles that of the forms which I now 
bring together under the name of Heterastr@a, in all of which, I 
may here observe, it is so very similar, that I do not find that it 
affords even so much as a specific difference. Vertical sections show 
how very similar it is in the several species. 
There are some of the species which have occasional calices which 
are almost as free on the calicular surface of the corallum as those 
of Elysastrea. Isastrea Murchisoni is one of these, and, as men- 
tioned by Prof. Duncan, some of the corallites are so much elevated 
above the others that there is “a faint trace of a subsequent growth 
of wall,” by which I presume it is meant that there is an addition 
made to the wall after it has been formed. As will be hereafter 
mentioned when speaking of the species, there is also rejuvenescence 
in Isastr@a Murchisoni, as there is in Elysastrea. 
Bearing in mind all the foregoing considerations, I have arrived 
at the conclusion that there is a rather near relationship between the 
Triassic genus Elysastrea and the so-called Liassic Isastrea and 
Septastrea, and that the latter are one and the same generically, and 
quite distinct from the later Secondary Isastree@ and the Tertiary 
Septastree. The genus into which I now propose to place the 
following species, I name and define as follows :-— 
HErerastRmA, nov. gen. 
The corallum is composite and massive, and the corallites are 
