138 MADKEroUARIA. 



Tablk IV.— analysis ANT) DISTRIBUTION OF THE MOKE EASILY 

 DEFINAI'.LE TYPES OF CALICLE. 



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

 {general habit from those of the Indo-Pacitic area. We have tractid th(! difference (see lutnj- 

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

 of the former area than in those of the latter. This tUfference has a somewhat remarkable effect, 

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

 plasticity ; its patterns are stiffer 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 tlie 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 metliod 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 wliich 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 all the Atlantic and West Indian forms except in what is known as the astneoid 

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

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



TJie 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 wlien 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. 



77(.c third ring is that of the wall granules or trabeculte, and are marked w^ in the 

 Diagram (B) — w^ being the wall gi-anule 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 

 impossible 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 gi-anules. 

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

 distance between the calicles. 



The fourth ririg 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. Ifi). The condition with a fourth ring, does however just occa.sionally occur (see 

 below). 



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



* On tho morphological importance of trabeculie in this genus, see Vol. V. p. 272. 



