122 MADREPORARIA. 



walls are variable in tiiickness ; where thinnest, they appear as a delicate, but pronounced 

 zigzag, elsewhere this is tliickened by the septal granules and synapticulae. These wall 

 elements are all slightly thickened, and contrast with the very delicate threads of the inner 

 ends of the septa and columellar tangle. The ring of pali is often complete, and stands up as 

 a conspicuous boss in the centre of the calicle ; seen sideways, the oval ring appears to 

 consist of four thick, lateral pali, the rest being thin, delicate, and rod-like. The columellar 

 tubercle is conspicuous, frequently flattened and extended across the calicle, as its median or 

 directive plane. 



The colour is duU grey, and its section shows an almost dense arrangement of long, fine 

 irregularly nodulated trabeculae. 



This coral compares in many respects with Porites x. IS, and appears to have belonged to 

 the same collection. The differences between them are most instructive, and as long as the 

 calicles are our chief guide we must keep them apart. We may later find some means of 

 analysing the structural features in a way which will enable us to recognise what are mere 

 accidental variations in calicle formation, and what are fundamental. 



a. Zool. Dept. 1906. 1. 1. 19. 



118. Porites x. 16. {Porites incertce sedis sextadecima.) (PI. VII. fig. 8.) 



[British Museum.] 



Description. — The corallum forms a massive irregular crest, which rises with a colony of 

 worm-tubes incorporated in its substance and opening over its surface. The mouths of the 

 tubes mostly bend over so as to lie on the surface of the coral, seldom looking outwards like the 

 calicles. 



The calicles are angular, depressed, 1 • 5 mm. in diameter. The walls are thin, mostly 

 with a whitish edge as if of powdered glass. The septa are short, thin, and granular as they 

 project from the walls some way below their upper edges. The pali are rather large, rough 

 granules, generally visibly associated with the primaries. The central tubercle is also rough 

 and granular, and often plate-like. On the lower parts of the coral the edges of the septa may 

 stand as granules away from the wall, and the intra-calicular skeleton may then appear to 

 consist of large granules not very crowded, and not reaching to the top of the wall. 



The colour is a pale buff, and the granules are either glassy, or whitish and powdery. 



Tliere is only one specimen. It is impossible to say what the special character of the 

 calicles is, or whether its growtli with worm-tubes is accidental, or a normal case of symbiosis. 

 Unfortunately no locality has been recorded which might act as a guide. While I regard it as 

 Indo-Pacific, I should find it hard to give any very definite reason for the opinion. There is 

 no other course open than to describe and figure it in hopes of its nearest allies being some 

 day discovered. 



a. Zool. Dept.1906. 1. 1. 20. 



