16 MADREPORARIA. 
We believe this to be a satisfactory explanation of the extra wall trabecula (wr), shown 
in Diagram C. The intervening row of costal trabecule here rise above the calicle apertures 
and form ridges, and thus reduce the tip of the ordinary wall trabecula (w) till it has the 
appearance of being an extra granule on the septal edge. This extra granule I call the wall 
granule. Pl. II. fig. 7, gives an instance of Porites calicles with a row of intervening 
trabecule flush with the surface, while Pl. V. fig. 8, shows such a row raised into a ridge as 
a false wall. 
As a rule the upheavals of this intervening costal tissue are most marked when the more 
or less rigid rectangular skeleton we have figured is melted down into a fluent network, which 
surges up as such into rounded knobs and ridges with a more or less woolly surface texture (see 
Pl. IX. fig. 5). The surface texture of forms with the rectangular skeletal reticulum is always 
granular, the granules representing the tips of the trabeculz. 
This preliminary sketch of the morphology of the skeleton of Porites enables us now 
to pass in review a few of its variations which in the following systematic survey have 
attracted most attention. But in doing so, I should like to say that, inasmuch as this sketch 
is one of the results of a critical analysis of the finished descriptions, which have already 
gone to press, it is possible that they may be so far incomplete in that characters the real 
signification of which have only come to light during this critical analysis may not have 
been detected, and it is now too late to undertake another seriatim study of the specimens. 
The Theca.—In the description given of the thecal skeleton of the related Goniopora it 
was stated that the wall was either simple or compound ; that is, it consisted of either one or 
more rimgs of trabeculz ; but it was suggested that the compound wall arose from the increase 
in the number of synapticule, between the septa, forming extra concentric rings round the fossa. 
There is no doubt that this happens, for as we shall see it happens in Porites, but the chief 
reason for the thick walls is undoubtedly that here given for Porites; if the calicles are not very 
crowded, intervening tissue appears, though in Goniopora without any attempt of this ccenen- 
chyma to surge up as it does at times in Porites * (cf. also Montipora). In Porites we certainly 
find both methods of wall thickening—by the intervention of tissue between the calicles, and 
by the appearance of a condition which Mr, Gardiner has called “Trimurate.” The wall is 
really simple, but the incipient synapticule, seen starting from the sides of the septal granules, 
may become complete and form an inner synapticular wall. When these inner rings appear on 
each side of the true wall (w) the wall appears to be 3 rings thick (ef. Pl. VI. fig. 1, and 
Pl. VIII. fig. 7). These two methods of developing reticular walls, each in its simplest 
condition consisting of three rows of trabecule, are quite distinct, and may be used as 
valuable characters. This point was unfortunately not clearly understood when the systematic 
portion of this volume was written. 
Most Porites show considerable variations in different parts of one and the same colony : 
thin walls are common, as a rule, at the rapidly growing surfaces, while down the slopes and 
* No indication of this upsurging was noted in Vol. IV., but I suspect a further and closer 
study might show traces of it. 
