46 MADREPOEARIA. 



In the other stock (/)), while the appearance of the horizontal section agrees fairly closely 

 witli that just described, the vertical section has a very different aspect. It appears to consist 

 simply of bundles of trabecule joined by horizontal bars, it being difficult at first sight to say 

 which trabecula3 are mural and which septal. Examination of the transverse section shows a 

 tendency in the septa to be lamellate, although most of them remain trabecular, and also 

 that the mural trabecula?. are the thicker. We cannot at present see why difference in rate 

 of growth sliould cause such differences of structure and texture. 



But two facts show that this is the chief cause: (1) on the slower growing incrusting 

 stock b the calicles on the highest ridge, and therefore those which are in most rapid growth, 

 approximate most to the calicles in the other stock a ; (2) on the stock with lamellate septa 

 the topmost calicles are much smaller, very crowded, and with frequently incomplete walls, 

 which are well-known signs of very rapid growth and multiplication. 



In all the specimens, while the skeletal elements are on the higher parts of the stock 

 smooth, they are rough and frosted in the lateral calicles. 



a (four fragments («i, a.^, «3, «■<) of a rapidly growing stock). Zool. Dept. 91. 3. 6. 96. 



b (slower growing stock). „ „ 91. 3. 6. 54. 



Compare the description of the next coral. 



13. Goniopora Tonga Islands (3)3. (PI. I. fig. 7 ; PI. XI. fig. 7.) 

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



t Goniopora parvistell a, Ortmann, Zool. Jahrb., iii. (Syst.) (1888) p. 158, pi. vi. fig. 3. 



BescriiJtion. — Corallum massive, like a shallow inverted cone, with the edges of the broad, 

 flat, convex top rounded off. Living layer extends under, but dies down a short distance from 

 the base of attachment. 



Calicles small, average 2 mm. on the top, where they are very deep, irregular in shape, and 

 angular. On the under surface the calicles average 2 • 5 mm., and about 1 mm. deep, angular 

 and largely drawn out of shape. The walls of the uppermost calicles are very ragged and 

 irregular and look thicker than they are, because their most conspicuous elements are the tops 

 of the lamellate septa, whose radial symmetry is obscured in spite of their conspicuous 

 developnieut. These tips of the septa are united together by a single, usually zigzag synapti- 

 cular wall with only occasional perforations, hence the walls are generally complete along 

 the edge. The septa appear in three cycles at the margin of the walls, but near the columella 

 the number is much smaller. Tliey show no traces of the typical septal formula. For the 

 sizes of the calicles they are thick and lamellate, usually coarsely toothed, a few in each 

 calicle are specially prominent at the margin. The radial symmetry is frequently disturbed 

 by two prominent adjacent septa being parallel to one another. A varying number of septa 

 (6-12), meeting at different angles, form an open axial columellar tangle. On this, incon- 



