POLYNESIAN PORITES. 89 
variations of structure assumed by Porites. There is no means of deciding whether they 
are specifically related—their variations being due to slight differences in environment—or 
whether they are all distinct species beginning to resemble one another from having to adopt 
the same method of life. If the pear-shaped growth form is due in any way to the environ- 
ment, which seems highly probable, then the similarity in the topmost calicles might be due to 
the tendency of the skeleton to rise in bundles of lamellx, a method of growth described 
in Vol. IV., p. 26, as not uncommon in the allied genus Goniopora. The coral above described 
is the only one of the four which shows a vertical section, and it is quite typical of the 
“expanding-sheaf” method of growth. Other examples of this method also occur in Porites, 
see Introduction, p. 21. 
Fig. 3 is from the top, and fig. 4 from the bottom. The minute pali are visible in these 
magnified photographs, 
a. Zool. Dept. 86.12. 9. 292. 
13. Porites Tonga Islands qo8, (Pl. II. figs. 5, 6; Pl X. fig. 6.) 
[Tongatabu, coll. J. J. Lister; British Museum.] 
Syn. Porites levis (non P. levis Dana), M.-E. & H., Ann. Sci. Nat. xvi. (1851) p. 27. 
Description.—The corallum consists of dichotomously branching stems, diverging at 
angles of 45° and less. The tips flatten and fork into two thick, blunt processes, while the 
portions of the stems between the divisions are usually swollen. The living stems may 
be 8 cm. long, with lower edges which creep rather freely; they rise from a tangle of fused, 
broken and rotting stems of earlier growths, the uppermost branches of which are either still 
alive or are capped with new colonies. 
The calicles are about 1°25 mm. in diameter, and, if slightly pitted near the tips of the 
stems, they are usually flush on the lower parts. The wall seems to be built of thick, flat, 
but rather scanty flakes, obscured by well-spaced, frosted granules, which rise upon them, The 
septa are conspicuous, and usually as in fig. 3, B, though with some uncertainty in the ventral 
triplet, which sometimes shows two, at others three, granules. These surface granules, 
which are the tips of the trabeculx, are important features; there are “intervening” granules 
(see p. 15), wall granules, septal granules, separated from the wall granules by a sharp, circular 
furrow; and within the ring of septal granules is a ring of pali which, especially the principal 
pali, are larger than the septal granules. The columellar tubercle is large and oval, or flattened 
in the directive plane. All the granules are finely echinulate or frosted. 
There are five specimens and a box of fragments of this Porites; the three largest rise 
from portions of the dead tangle of previous growths; the stems forming this tangle are 
mostly greatly corroded, and seem to have fallen over (see figures showing growth-form), The 
calicles in all the specimens are of the same type, but differ in the height and width of the 
walls. But as these may vary on the two sides of one and the same stem, they afford us no 
basis for further subdivision. 
