24 



BRITISH FOSSIL CORALS 



" Corallura very dense, and not bearing columnar processes, as in the preceding genus. 

 Calices polygonal, columella styliform, not projecting much. No pali. Septa thick, 

 apparently eight or ten systems, two or four of the secondary septa being as much 

 developed as the six primary ones. Walls thick and united as in Stylocoenia." 



M. de Fromentel separated the genera Astrocoenia and Sti/loccenia, and retained the 

 latter amongst the Eusmilince aggregate. There was no reference made, therefore, in his 

 generic diagnosis of Astrocoenia to the genus Stylocoenia. M. de Fromentel's descrip- 

 tion of the generic peculiarities of Astrocoenia are as follows : " Corallum massive, com- 

 posed of corallites united by their walls, which are prismatic in shape ; the calices are 

 polygonal ; the columella is styliform, and more or less projecting ; the septa are tolerably 

 thick, are few in number, and are dentate, especially near the columella ; there are no pali." 



Whilst investigating the Madreporaria of the Maltese rocks in 1865, I found that 

 the septa of the common species Stylocoenia lohato-rotundata, Mich, sp., were dentate.' 

 The species occurs also in the Chert of Antigua, and presents there the usual plain septa 

 considered to mark the family of the genus. If fossilization can remove the dentations 

 of the septa of one Stylo cvenian^ it can do so in others, and it may be safely asserted 

 that all the Sfylocoenians had dentate septa. 



This dentate condition of the septa brings the genera Astrocoenia and Stylocoenia 

 together again, although it removes them from the Eusmilince into the Astrceacede. 



MM. Milne-Edwards and J. Haime's generic description can thus stand, and its 

 concluding sentence respecting the thick walls of the genus which was omitted by M. 

 de Fromentel is very important. 



In some species, as in A. pulchella, Ed. & H., the calices are so wide apart in some 

 specimens, and in certain spots in all the specimens, that there is evidently here and 

 there a ccenenchyma between the walls of the corallites. The surface of the ccenenchyma, 

 which appears to arise from an hypertrophied condition of the adjacent corallite walls, is 

 usually ornamented either with prolongations of the costae, or with small papillose granules. 

 This is observed in other species, and it is noticed that the amount of ccenenchyma 

 varies according to the shape of the corallum, and the rapidity of the multiplication of 

 the corallites. The presence of scattered granules, or of small papillae on the coenenchymal 

 surface, and between the external terminations of the costae, is observed in some speci- 

 mens of a species, and not in others ; but the costae, although they may extend far over 

 the inter-calicular spaces (or, in other words, over the surface of the ccenenchyma), never 

 unite, and run into those of adjoining corallites. There are modifications in the length and 

 straightness of the costae, and where there is no ccenenchyma, and the walls of the corallites 

 are thin, they may be so reduced in size as to appear to be simple terminations of septa. 



In many species the ccenenchyma, when non-costulated, and not ornamented with 

 granules, becomes slightly ridged, and foreshadows the condition which peculiarises the 

 genus Stylocoenia. 



' ' Ann. Mag. Nat. Hist.,' April, 1865. 



