Madreporarian Genus Astreopora. 275 
Earliest known Stage.—The youngest colony discovered (on 
the dead portion of a larger specimen *) is a minute plate- 
like growth of ccenenchymatous reticulum, not quite 3 millim. 
in longest diameter. ‘There is a central calicie (the parent 
calicle of the colony), readily distinguishable by its size, and 
an irregular ring of smaller (daughter) calicles. ‘The whole 
is contained in a saucer-like epitheca, with edges bent up all 
round free of the substratum. The colony has apparently 
grown unsymmetrically ; instead of being a complete circle, 
the corallum has spread out symmetrically only on one side 
of the parent calicle, as shown in the figure (Pl. XIV. fig. 1). 
There are two cycles of septa, the first being conspicuous. 
The daughter calicles develop in the ccenenchyma, and one (a) 
is seen at the extreme edge of the colony, part of its wall being 
formed by the epitheca. There is no connexion between the 
calicles other than the canal-system of the coenenchyma. 
The typical structure of the coenenchyma is not visible at 
this stage; it can only be detected in the larger specimens. 
Later Developments. — Comparison of adult specimens 
showed that there are at least three fairly distinct methods of 
growth, according to which such an initial colony as that just 
described may develop further. I have therefore divided the 
genus primarily according to the methods of growth. 
First Method of Growth: Explanate-—The corallum ex- 
pands chiefly laterally, the growth in thickness being slow 
and irregular. The epitheca continues to grow and to support 
the edge of the corallum. ‘The most perfect example of this 
is Briiggemann’s species Astrewopora expansat, which is 
purely explanate, the thin expanding edges rising freely but 
gradually from the substratum, accompanied and supported 
by a well-developed concentrically wrinkled epitheca. ‘The 
calicles are far apart and for some distance from the edge 
appear, on being held up against the light, to penetrate right 
down to the epitheca. 
Another but less perfect example is Lamarck’s myrioph- 
thalma, which forms large plates; these, when young, may 
be thin and flat, but when old become irregular and humpy, 
ultimately forming great mounds as successive growths creep 
over their uneven predecessors. ‘There is in the collection a 
good series showing these changes; but for the presence of 
the intermediate growths the oldest and youngest specimens 
would almost certainly be classed as distinct species. 
In this and other explanate forms the relation between the 
epitheca and the expanding edges is of considerable interest. 
* The registered number of which is 91.5.6.54. 
+ Ann. & Mag. Nat. Hist. (4) vol. xix. p. 416. 
20* 
