R. F. Tomes—On Heterastreea, Lower Lias. 209 
diameter, and thus it forms actually one low inverted cone upon 
another. This peculiarity (probably an occasional result of the 
exhaustion which follows reproduction) cannot properly be con- 
sidered a generic distinction.” 
In his “Structure and Classification of Zoophytes,” page 65, after 
speaking of the process of dying or removal below, he says, “ It is 
obvious from the preceding, that the polyp, which is the germ of a 
compound Zoophyte, loses its identity, and cannot be said, in any 
proper sense, to have the long life which is attributed to the full 
erown Zoophyte itself; or else we might have among the huge 
Astraeas of the Red Sea, polyps that were contemporaries with the 
builders of the Pyramids.” The polyp, however, ‘which is the 
germ of a compound Zoophyte,” may lose its identity, and most 
likely does, by the process of gemmation, but not by rejuvenescence, 
which under no circumstances, as explained by Milaschewitsch, 
increases the number of corallites, and it is certainly rejuvenescence, 
of which Dana was then speaking. 
It is when the contraction of the polyp takes place very irregularly, 
that the true nature of the process becomes most easily determined. 
If the shrinking of the soft tissues of the polyp is wholly on one side, 
and very great in degree, so that the visceral cavity is drawn out 
of the centre of the calice, then the constricted side of the animal 
will be lifted out of the loculi in the process, but that side which 
has undergone no such contraction may be very little interfered 
with. In such a case entirely new septa will be formed on one 
side of the now-expanding calice, while on the other side, no new 
ones will be produced, nor indeed needed, the old ones being still 
in actual use. The contraction may, however, be, and it often is, 
just sufficient to leave vacant only those loculit which have been 
formed by the later developed septa, and then there will be the full 
number of cycles on one side, while on the other the primary septa 
only will be present. 
As observed by Dana, rejuvenescence is not of generic importance, 
and he might have said that it had no specific value, in which 
respect it differs widely from gemmation, which has not only specific 
but great generic value. 
The Madreporaria of the Trias are very little known in this 
country, and beyond a few species which occur in the Sutton Stone 
of the Glamorganshire coast, we have to refer chiefly to Laube’s 
descriptions and figures of the St. Cassian species. An examination 
of the compound genus Elysastrea reveals a very curious septal 
arrangement. This I will now proceed to consider, and it will be 
desirable that I should, in the first place, quote from Laube some 
part of his generic description. He says that gemmation takes 
place within the calice, and resembles that of Heliastrea.'_ He then 
goes on to state that the young individual separates itself by a little 
1 MM. Milne Edwards and Haime define the budding in Heliastrea in the 
following words: ‘‘ Les nouveaux individus produits par bourgéonnement se montrent 
dans les differents espaces intercalicinaux.’’ Probably gemmation in Elysastrea 
also took place in the intercalicular spaces. 
DECADE III.—VOL. V.—NO. V. 14 
