274 _ MADREPORARIA. 
B. Those in which one extra trabecula (wr in the diagram C) typically—that is, where 
the calicles are not specially crowded—appears between the wall trabecule w of adjacent 
calicles. 
C. Those in which the wall trabecula, marked w in the diagrams, forms the middle line 
between adjacent calicles. Those of the one calicle then appear to be arranged alternately 
with those of its adjoining calicles, as we gather from the fact that the connecting synapticulz 
frequently form a zig-zag line. In the Introduction it was assumed that this zig-zag line 
indicated some interval between the calicles, but it might also indicate the opposite, namely, 
a crowding as to lead to a kind of interlocking. 
D. Those in which the skeleton has melted down into a fluent reticulum, or in other 
ways become so modified in its texture that trabecule are no longer sufficiently pronounced to 
be of use for either of the previous divisions. All these cases may be regarded as secondary, 
because vestiges of the trabecule can nearly always be made out. 
A. The Cenenchymatous Forms (Synarea of Authors). 
y Y 
These cannot form a separate genus, for two reasons: (1) they show no essential structural 
difference from ordinary Porites, the septal and palic formule are the same in both, and in the 
matter of wall formation they intergrade with the rest of the genus; and (2) in this very 
difference in wall formation they show no single definite plan or method of specialisation of 
their extra-costal trabecule which might entitle them to a separate place. The variations run, 
as it were, in all directions: they only agree in the fact that they are Porites with an irregular 
number of costal trabeculee involved in the composition of the wall. 
These specialisations may be perhaps divided as follows : 
a. With walls of uniform or nearly uniform width. 
i. The walls remain smooth over the whole of the level surface. 
P. North Australia 1. 
P. Amirantes 1, Perhaps a young form. 
ii. The walls remain smooth but the surface of the colony rises into smooth, 
usually angular, ridges and crests. 
P. Fiji Islands 9. Colony rises into angular branching processes. 
P. Fiji Islands 14. With wall-trabecule obscure, appearing at the 
surface as granules. The horizontal elements somewhat arched. 
P. Fiji Islands 15. With pali and wall-trabecule pronounced. 
P. Great Barrier Reef 10. With pali taller than the wall-trabecule (ct. 
P. Red Sea 4). 
P. Philippines 2, With pali taller and larger than the wall-trabecule 
(cf. P. Red Sea 4). 
iii, The walls rise everywhere into inter-calicular ramparts and gyrating ridges. 
P. Society Islands 2, The inter-calicular ridges are sharp and ragged 
edged, with trabecule disguised and horizontal elements pronounced 
and tilted into ragged flakes. 
