50 MADREPORARIA. 
22. Porites Fiji Islands 4%. (P. Fidjiensis septima.) (PI. III. fig. 9; ef. Pl. XIII. 
Diagram fig. 8.) 
[“ Fiji Reefs,” coll: H.M.S. ‘ Challenger’ ; British Museum. | 
Syn. Porites arenosa (partim) Quelch (non Esper), Chall. Rep. xvi. (1886) p. 183, 
Deseription.—The corallum appears to have formed a thick, flat cake, with level but 
slightly wavy top, and slightly bulging sides, which are thick, round, and project over the 
substratum. The whole mass is over 5 em. thick, and the living colony extends some 3 cm. 
round and under the edge. 
The ealicles are small, 1 mm. in diameter and under, and about 0°5 mm. deep. The 
walls have conspicuous median ridges consisting of single, usually straight rows of stout 
trabecule which are sometimes separate, in which case the ridge consists of a row of large 
square granules. In the angular calicles in the valleys these trabecule alone form the walls, 
but on the wave-like mounds of the table-top the septal granules swell and fuse to form a 
second wall inside the wall trabeculee. Where the surface has been abrased, the whole 
thickened wall is very stout and almost solid. The septal formula is complete, but the septa 
contrast greatly with the stout walls; they are thin, glassy and fragile, and in all the deeper 
calicles project from different levels, so as to appear often quite irregular and with hardly any 
development of pali. In the shallow calicles on the under surface the walls are broad, flat, 
smooth flakes, which send long tongues with jagged edges sloping down each side into the 
calicles, radially symmetrical ; and, in addition to the large frosted pali and the granules of 
the median ridge, are distinct traces of both wall- and septal-granules, with a central 
columellar tubercle almost on a level with the pali. In the deeper calicles this tubercle is 
only seen deep down connected by radial elements with a columellar ring, which is, however, 
at a still lower level. 
The single specimen is only a fragment—apparently a large chip from the projecting 
edge of such a stock as that described and represented diagrammatically on IAL UL, ie, &. 
There is not much of the top surface shown; there is a complete vertical section at least 
down to where the corallum is destroyed by a boring sponge. In this section the thick wall- 
trabecule can be distinguished from the thinner elements of the intra-calicular skeleton. 
The growth-form is like that of P. Fiji Islands 4, but the edges are thicker and rounder. 
The photographs will show the differences between the calicles and those of P. Pye Islands 2, 
with which Mr. Quelch placed it as Esper’s “ arenosa.” 
a. Zool. Dept. 86. 12. 9. 362. 
