138 MADREPORARIA. 



Table IV.— ANALYSIS AND DISTRIBUTION OF THE MORE EASILY 

 DEFINABLE TYPES OF CALICLE. 



As already explained in the Introduction, the calicles of these West Indian Pontes differ in 

 general habit from those of the Indo-Pacific area. We have traced the difference (see Intro- 

 duction, p. 13) to the fact that the skeletal elements are all coarser and thicker in the Pontes 

 of the former area than in tliose of the latter. This difference has a somewhat remarkable effect, 

 for the size of the calicles remaining about the same, the extra thickness robs the skeleton of its 

 plasticity ; its patterns are stififer and rougher, and there is consequently less delicacy, 

 regularity, and symmetry than is the rule with the calicles of the Indo-Pacific forms. As an 

 illustration, compare the first figure on Plate I., which belongs to the Indo-Pacific group, with 

 those immediately following it, which are all of Atlantic specimens. 



Taking a glance at the calicles as seen in the Plates I.-VI., it is at first sight difficult 

 to find any character which seems to have stability enongh to supply us with any taxonomic 

 character. We have therefore to fall back upon the method of classification adopted in 

 the Table III. in Vol. V., p. 258. This was based upon the number of rings of trabecular 

 round the central tubercle, because, however irregular, they could be counted in all cases 

 except those in which the whole skeleton was melted down into a confused network ; and, 

 further, they clearly referred to characters of prime morphological importance.* 



The innermost ring is that of the pali which are generally well but irregularly developed 

 in aU the Atlantic and West Indian forms except in what is known as the astrseoid 

 group ; the chief characteristic of this latter group being the large open fossa with only 

 scant traces of pali deep down (see below, p. 142). 



The second ring is that of the septal granules, which are very variously developed and 

 indeed chiefly recognisable in a long comparative survey. They are but seldom mentioned 

 in the systematic descriptions because they are in themselves so unobtrusive, yet when the 

 whole series is compared in the way here proposed according to the rings of trabecular, they 

 become of great importance. This' was exactly our experience in Vol. V. 



The third ring is that of the wall granules or trabeculse, and are marked w' in the 

 Diagram (B) — vr' being the wall granule of an adjacent calicle in all these forms with simple 

 zigzag walls. In Vol. V. p. 273, some doubt was expressed as to whether the thickness of 

 this zigzag — not as a line but as a system — might not just as well indicate the depth to which 

 the calicles were interlocked as the distances they were apart as units of the colony. The 

 confusion of the skeleton is often so great that the exact relationships are frequently 

 impos.sible to make out, but in all cases in which among these West Indian forms the 

 elements are clear, the wall granules always belong to the same septum as the septal granules. 

 This leaves no doubt that the thickness, or rather the depth, of the zigzag represents the 

 distance between the calicles. 



Ths fourth ring is but very seldom developed in these West Indian Porites. For even 

 where their walls are reticular, the reticulum is mostly due to the fact that a separate ring of 

 tissue unites the septal granules producing the condition which Gardiner has called Trimurate 

 (see Vol. V. p. 16). Tlie condition with a fourth ring, does however just occasionally occur (see 

 below). 



The fifth and higher rings which occur in great abundance among the Indo-Pacific forms 



* On the morphological importance of traljeculse in this genus, see Vol. V. p. 272. 



