62 Mr. J. Thomson and Dr. H. A. Xicliolson on the 



The central tabulate area of the coral is, in all forms pro- 

 perly referable to Gyatliophyllumj surrounded bj an exterior 

 zone of finely vesicular tissue. This forms the periphery of 

 the visceral chamber, and is composed of numerous layers of 

 minute lenticular cells, which are invariably inclined upwards 

 and outwards as re2:ards the axis of the coral (PL VI. fig. 1 A, 

 & PI. VII. figs. 7 a, 9 a). 



The septa are well developed, symmetrical, regularly ar- 

 ranged, and not interrupted in general by the development of 

 any conspicuous fossula. Secondary septa may or may not be 

 present. In the outer portion of the coral the iuterseptal 

 loculi are more or less copiously filled up by dissepiments, 

 which form the vesicular tissue above spoken of, and have 

 their convex surfaces directed upwards. The sides of the 

 septa are plain, and their free edges are not denticulated as 

 they are in the genus Heliophyllum. At the bottom of the 

 calice the septa generally extend inward to the centre of the 

 visceral chambers, where they are usually twisted together so 

 as to form a small projection or false columella. In almost all 

 the typical forms of the genus a similar meeting of the septa 

 in the centre of the corallum is shown in transverse sections 

 of the coral at all heights (PI. VII. figs. 8 & 9). In some 

 forms, however, which are not otherwise separable from Cya- 

 ihophyllum^ and which appear properly to belong to it, trans- 

 verse sections exhibit the septa stopping short at some distance 

 from the centre, and leaving the tabulae exposed to view over 

 a larger or smaller median area (as in C. jparacida, M'Coy, 

 PI. VII. fig. 7 b). 



It will be seen fi-om the above that the structural characters 

 which collectively distinguish the genus CyatliopTiyllum are : — 

 (1) the presence of a more or less extensive central tabulate 

 area ; (2) the existence of an exterior zone of vesicular tissue, 

 formed by oblique dissepiments, the convexities of which are 

 directed upwards ; (3) the more or less completely developed, 

 symmetrical, and plain septa ; (4) the general twisting together 

 or union of the septa in the centre of the floor of the calice, 

 constituting a false columellar projection. 



With regard to the affinities of the genus, its nearest ally 

 appears to be Diphyitliyllum^ Lonsd. Some forms of Cyatho- 

 iphyllum^ indeed, such as C. ccesintosum^ Goldf., appear to es- 

 tablish an almost complete transition between the two genera. 

 As a general rule, however, the genus Dijjhyphyllum can be 

 readily distinguished by the fact that the septa appear never 

 to extend quite to the centre of the visceral chamber, but 

 invariably leave a well-defined central tabulate area into which 

 the septa are not prolonged. There is thus no twisting to- 



