POLYNESIAN PORITES. 37 
10. Porites Tonga Islands qao5. (P. Tongaensis quinta.) (Pl. Il. fig. 1; Pl. XIII. fig. 5.) 
[Tongatabu, coll. J. J. Lister; British Museum. ] 
Description—The corallum, like the preceding form, is a knob which envelops the tips 
of branching corals; its surface is smooth, and the lower margins of the colony seem to die 
regularly upwards without the formation of creeping edges. 
The calicles, about 1 mm, in diameter, are nearly flush with the surface. The walls are 
straight on the flattened top, and are either extremely thin and friable with straight or 
ragged edges, or thickened and reticular, owing apparently to the addition of a regular or 
irregular ring of synapticule on each side; this thickening may be confined to single sides and 
wall-angles. The septa in the uppermost calicles are very thin, fragile, perforate plates, slightly 
bent, and with jagged surfaces. They seem to be arranged most often as in fig. 3, B, but the 
ventral triplet shows irregular fusions. In the calicles round the lower parts of the stock, 
with thickened skeletal elements, the septa are also thickened, and the pali, which in the 
uppermost calicles are slightly frosted or branching points, are round, frosted granules. 
The columellar tangle seldom forms a complete ring beneath the pali; its elements are 
more often arranged radially round a small central tubercle. 
This coral must certainly be allied in some way both with that which precedes it and 
with that which follows it. Their growth-forms, and the structural types of the calicles, are so 
much alike that it is quite puzzling to find such diversity in detail. A comparison of the 
figures will show at a glance how great these differences are. The whole stock is 6 cm. high, 
and the living layer extends about 3 cm. down the sides. 
The figure is taken from the flattened top of the stock. 
Compare observations on this growth-form under P. Tonga Islands 7. 
a. Zool. Dept. 1904. 10. 17. 4. 
11. Porites Tonga Islands ao)6, (Pl. Il. fig. 2; Pl. XIII. fig. 6.) 
[Tongatabu, coll, J. J. Lister; British Museum. | 
Description.—The corallum forms pear-shaped knobs, with wavy surface, but not, as in the 
two preceding forms, round the branches of other corals. This coral started as an encrusting 
colony, and rose in the centre. The colony extends but 3:5 cm. down the sides with only slight 
edge-formation, here overhanging, there dying upwards with formation of epithecal films. 
The calicles are superficial, angular to subcircular, and slightly over 1 mm. in diameter. 
The wall-ridges are very thin and membranous, but irregularly bent into zigzags, and so porous 
that the edges are ragged and interrupted; here and there they are reticular, especially when 
the circular calicle is surrounded by an angular wall-ridge; then the corners of this area are 
