POLYNESIAN GOXIorok.i;. 45 



12. Goniopora Tonga Islands (3) 2. (PI. I. fig. 6 ; PI. XI. fig. G.) 

 [Tongatabu, coll. J. J. Lister ; British Museum.] 



Description. — Corallum appears to be built up of smooth cushion-shaped masses capping 

 similar but smaller growths. The cushions are large and thick. 



Calicles vary greatly in size in different parts of the same mass, from 3 ■ 5 mm. to 2 • 5 mm. 

 and about 2 mm. deep. The walls over all the upper parts are thin, friable, incomplete, and 

 very perforate, the thin synapticuhe running in a pronounced zigzag. The 24 septa rise as 

 thin pointed lamelhe, often free, that is, not joined by synapticuhe, and making the surface look 

 bristly. The primaries and secondaries alone slope inwards to the columellar tangle, the 

 tertiaries remain rudimentary. Denticulations of their inner edges bend up as tall, delicate 

 pali in the uppermost calicles. But in the lateral calicles the pali form a clear ring or oval 

 of six, with frequently a central fossa. The interseptal loculi are large, owing to the tertiaries 

 remaining rudimentary. 



Very delicate tabulae are numerous and the corallum is light and porous ; the transverse 

 section is composed of radial groups of lamellate septa joined by inconspicuous synapticuhe. 

 The ragged inner edges of the septa are seen to interlace to form the columellar tangle. 



We have here clear indications of an approach to the sheaf-method of growth, combined 

 with the pulvinate method of growth of the last form, the successive cushions of which seem 

 to grow slowly and are trabeculate in structure. In this coral they grow very fast, and 

 the lamellate septa shoot up like spikes all over the surface, making a considerable difference 

 in the aspect of the calicles (cf. PI. I. figs. 5 and 6) and in the general characters of the stock. 

 Yet it is obvious that the differences might be referred to rapidity of growth due to some 

 accident of the environment. 



Taken together the forms show a most instructive transition between the ordinary convex 

 growth of the pulvinate type, and the expanding column of the typical sheaf formation (cf. 

 figs. C and E, Introduction, p. 24). 



There are five specimens and fragments included under this heading. Four are frag- 

 ments of probably one large stock (a) ; three of these actually fit together, while the fourth 

 contains fragments of the same madrepore overgrown by the others. The other specimen b 

 (see PI. XL fig. 6) is somewhat different from (a), and in the direction of the coral last 

 described — and as there stated the differences may be due to variations in the rate of growth. 

 The corals a and b agree (1) in the character of the calicles, (2) in the curious crimped or 

 wrinkled walls formed of the tips of the radial septa joined by very thin, often zigzag synapti- 

 cular bars, (3) in the number of the septa, and (4) in the group of prominent pali frequently 

 surrounding a small central fossa. They differ chiefly in their vertical sections. The one (a) 

 which appears to have grown most rapidly and has incorporated branches of madrepores, is in 

 section little more than a sheaf of narrow lamellate septa. Further, as stated in the description, 

 the horizontal section shows little more than star-shaped groups of lamellate septa, the thecal 

 tissue being reduced to a thin often zigzag thread. 



