118 MADRErnUARTA. 



112. Porites .r 10. (Poritrf! Inrrrt.w .wlis iJrcimn.) (PI. VII. fi^. 2 ; PI. XVII. fig. 12.) 



[British Museum.] 



Description. — Tlie coralhini grow.s out into flat, horizontal, dish-like leaves, free for 20 

 cm. and more, and supported to the edge by epitheca ; they are 1 mm. tliick at the growing 

 edge, 11 to 12 mm. near the attachment of the old stock. The living layer extends some 

 10 cm. inwards from the edge ; the central part within the living layer in large stocks is 

 dead and often partly arched over by fresh layers. About 1 cm. from the free margin, 

 concentric rows of ccenenchymatous pustules make the surface uneven. These are submerged 

 as the coral thickens. 



The calicles are superficial, very ill-defined, about 1 mm. near the margin, but to the 

 naked eye extremely minute, as irregular Ijreaks in the smooth granular surface. The smooth 

 flat ccenenchyma (= fused walls) is covered with tall, slightly branching granules, rather 

 wide apart and giving the surface a dusty appearance. Beneath these granules the texture is 

 composed of flat flakes. The calicles are rendered visible chiefly by the grouping of the septa, 

 which differ from the surface granules only in size and arrangement and may be here and tliere 

 very slightly exsert. They are completely united in four pairs and a triplet in the typical 

 manner, and the five pali or exsert inner edges of the septa are frequently V-shaped. The 

 septal granules are very irregularly developed ; in the younger calicles occasionally they may 

 unite with the pali, but in the older calicles the granules of the walls and the pali are joined 

 by a ring of septal granules. The central fossa is a mere pin-hole, in which a minute colu- 

 mellar tubercle may be just visible. The ccenenchymatous pustules have a texture sUglitly 

 different from that of the level surface ; there are no granules anil the surface is reticular, but 

 smooth, dense, and with microscopical pores. Calicles open on the larger of these elevations. 



Foliate Porites have not been hitherto known, and this is the most pronounced of the 

 forms now discovered. On its method of growth-form, see p. 137. 



In Table III. Vol. V. and on p. 259, a list of all the foliate Porites so far recorded is 

 given with their localities. This one, which is by far the most remarkable of all, not only in 

 its growth-form but also for its other structural features, has unfortunately no recorded locality. 

 It is a ccenenchymatous Porites. Under the older system it would have been classed as a 

 Si/narcea, see Vol. V. pp. 9 and 274. 



On the dead part of this coral is a young specimen as a small hemispherical colony, con- 

 sisting of a central larger'parent calicle (0 • 75 mm. across) and a ring of five smaller daughters. 

 Tlie calicles all gape open, and the septa, hardly traceable down the sides, yet stand up round 

 the edge on the top of the wall, very irregularly, liut apparently in two cycles. One of the 

 most interesting features is the presence of pronounced directives in some of the daughters, and 

 these directives are in vertical i)]anes, radially symmetrical with septa or costal of the parent. 



While it is probable that any young colony of Porites found round the base of a large stock 

 is an offshoot of that stock, it is often quite impossible to say from any structural features 

 whetlier this is the case or nut. There is abundance of evidence that stocks only gradually 



