POLYNESIAN PORITES. 41 
14. Porites Tonga Islands (19)9, (PI. II. fig. 7; Pl. X. fig. 7.) 
[Tongatabu, coll. J. J. Lister; British Museum. ] 
Description.—The corallum forms low dense tufts of short, thick, curving branchlets, 
which sometimes rise from an expanding base; the stems fuse freely together, and the colonies, 
as in the last case, rise from a tangle of dead and often overturned previous growths, and may 
thus be without firm attachment to the substratum (see the figures of growth-forms). 
The calicles, as in the last form, depend upon the arrangement of the surface granules ; the 
chief differences are due to the persistence in this form of a wall-ridge. This ridge, though very 
slight, is sharply raised above the otherwise smooth surface at the tips of the stems, and is 
traceable over the whole stock as a polygonal network. The broad flat flakes of the walls 
below the surface granules are so perforated as to be almost a filamentous reticulum, and con- 
sequently the granules upon them, which are destined to construct the next flake layer, are not 
so solid as in the last form, but more branching and feathery. On each side of the median 
intervening * granules is a row of large distinct wall-granules, within which is a ring of septal 
granules round the pali; all the granules are delicate, feathery, and well spaced. The palic 
formula (fig. 3, B) is regular and complete. The principal pali are large and oval. The central 
tubercle is flattened in the directive plane. 
This coral is certainly closely related to the form last described. Its short stems flatten 
and divide, the two forks, as in P. Tonga Islands 8, being short, thick, and flat-topped. The 
difference in the growth-form is, perhaps, sufficient to account for the difference in the calicles, 
for the stems being so much shorter do not require the skeletal elements to be so stout ; hence 
the trabeculae seen in the transverse section are thinner, while again the thinner trabeculz account 
for the better spacing of the granules. This form may then be regarded as a stunted variety 
of the foregoing ; that it is not merely an individual variation we gather from the fact that the 
dead overturned stocks on which it grows are similarly stunted. 
The living layer is not more than 5 em. deep; its lower edges seem to creep rather freely. 
On such encrusting edges the sharp raised wall-ridges appear round the calicles. The photo- 
graph, again, shows no traces of the horizontal tissue beneath the layer of granules. 
a, b. Zool. Dept. 1904. 10. 17. 11. 12. 
15. Porites Tonga Islands 010, (PI. Il. fig. 8; Pl. XI. fig. 1) 
[Tongatabu, coll. J. J. Lister; British Museum. | 
Description.—The corallum forms rather open clusters of thin, slightly tapering stems, 
which fork dichotomously, though somewhat irregularly. The branchlets mostly have a faint 
* See Introduction, p. 15. 
a 
