INDIAN OCEAN PORITES. 191 
irregular, and seems to have a great many small square meshes, asif the filaments met at right 
angles. The septa are also extremely thin, and start well below the top edges of the walls, 
sloping inwardly and downwards. The pali are conspicuous, the four lateral principals being 
large and well developed. The directive pali are often very small, the ventral triplet being 
either fused or separate. Owing to the delicacy of the septa, the fossa and interseptal loculi 
are very open, and far down delicate skeletal strands can be seen forming an open columellar 
tangle, joining the pali and central tubercle together ; the last named is very small, sometimes 
thin and flattened, and far down. 
The section is trabecular, with a strong tendency in the trabecule to be lamellate. 
A rapid thickening takes place in the skeletal elements, so that the coral mass is a dense, close 
reticulum. 
The colour is a light brown. 
There is only a chip of some massive form, which Mr. Andrews says was very abundant 
and also very amorphous, taking on any shape according to its position. The skeletal elements 
of the surface are so fine and delicate that the coral has a soft woolly appearance. Such an 
appearance is seen also on P. Bay of Panama 1, but a comparision of the figures, Pl. X. fig. 3, 
Pl. XXVIII. fig. 9, shows them to be very different specialisations of the generic type. 
This small specimen was referred to by me in the Proc. Zool. Soc. 1900, p. 123, and it was 
suggested that it might be related to P. Ceylon S, which I had then proposed to call P. Indica. 
a. Zool. Dept. 99. 5. 12. 25. 
In addition to this chip from a recent form, said to be plentiful on the shores of the 
Island, there are a number of fossil fragments from the sea- and inland-cliffs. There is no 
apparent affinity between any of these fossils and the form just described. The former seem 
to fall into three groups, differentiated chiefly by the thickness of the walls. In the one set, 
the walls are thin and simple; in the other, reticular. The former seem to agree roughly with 
the group which Professor Gregory * called “ Porites aff. lutea M.-E. & H.” and the latter with 
Professor Gregory’s “ Porites belli n.sp.” 
The majority of the specimens are shared between these two divisions. In addition, there 
is a single specimen differing from these in that the polyp cavities are not traceable through 
the section. 
The classification of recent Porites is based wholly upon the fine structural details of the 
calicles on the surface. These are lost in the vast majority of fossils, and only the sections 
remain to be compared. These can show no traces of surface characters, for not only is the 
relief gone, but the skeletal elements below the top surface are always secondarily thickened as 
part of the growth process. [f it is difficult to enter into the specific relationships of the 
recent forms, it is quite impossible to pretend to any knowledge of those of fossil forms with 
no surface preserved. 
* © Monograph of Christmas Island,’ C. W. Andrews (1900) p. 206. 
