INDIAN OCEAN PORITES. 217 
sometimes to the pali. The septa themselves are either thin and short, or horizontally 
flattened and curving as offshoots of the synapticular shelf. The pali rise to the level of the 
wall : the five principals as frosted knobs, like the septal granules. The dorsal directive has 
either no knob, or a very minute one. The fossa seems to be early filled up by flaky tissue, 
from which a small central tubercle rises, but not to the height of the pali. 
Low down on the sides of the stock the median wall sinks, the shelves greatly widen, 
and the walls are thick and built of stout flakes; the septa become broader, and the granules 
and pali larger and coarser. 
There is no available section, and the colour of the unbleached stock is a light yellowish 
brown. 
There is, again, only one specimen of this beautiful Porites. This form of the synapticular 
shelf is, so far, unique. 
a. Zool. Dept. 91. 4. 9. 37. 
224. Porites Diego Garcia 38. (P. Garciana tertia.) (Pl. XXXII. fig. 3; Pl. XXXIV. fig. 4.) 
[Diego Garcia, coll. G. C. Bourne; British Museum. ] 
Description.—The corallum rises as a close cluster of short, thick, often flabellate 
stems. This gradually expands into a wider and more open arrangement of thinner flabellate 
branches, which again fork. Before doing so, the branchlets usually taper rather suddenly, 
and then swell into small knobs which flatten, the compression being in the plane of that 
of the branches. The successive forkings follow one another every 1°5 em. of upward 
growth, so that the fan-like expansion of the branches is rapid and open. The living layer 
reaches here and there to 8 em. 
The calicles are 1 mm. in diameter, flush with the surface, and sub-cireular. The walls 
show an elegant arrangement of flat flakes, with round perforations and crisp edges; from 
the surfaces of the flakes thin threads, points and straggling plates arise, and give the surface 
a velvety appearance. The tips of these surface upgrowths expand and form the next layer 
of horizontal wall flakes. The septa are not visibly tongues of the wall flakes, but show 
characters more like the thin plates which rise on the walls, only they tend to swell into 
rings of septal granules and pali. On the lower parts of the stock these become large and 
very finely echinulate. Neither of these rings is quite symmetrically round or oval, the 
directives being nearer the periphery and interrupting the curve. The complete palic formula 
is frequently present ; the triplet, however, is irregular. There is a flattened central tubercle. 
The section shows a system of very stout trabecule, rather loosely arranged, and with 
distinct but not very stout horizontal or concentric elements. The colour of the unbleached 
coral is a warm brown. 
The chief point of interest in this coral is the fact that it combines the two characters of 
branching Porites described in the Introduction, p. 21. The horizontal elements are con- 
2F 
