412 ON THE MADUEPORAIUAN GENUS I'HYM ASTR.EA. [Juiie 19, 



Sections of the corallutn must cut across corallites at different 

 angles to their long axes ; and the appearances presented here and 

 there, although perfectly explicable in the perfect specimens, might 

 be mistaken" for fissii)"arous calicular division. The appearance 

 of the sections reminds one of that of many fossil corals which 

 have weathered, or which have been partly preserved, or which are 

 offered to the student in sections. The truth could not be ascertained 

 from such relics. 



VII. The Affinities of the Genus with others of the Recent 



Coral-fauna. 



The genus PhijmastriBa would be very isolated in the classifica- 

 tion were the two original species the only ones ; but the new species, 

 on which the costse are tolerably well developed, allies it to Ile/iastrcsa. 

 It does hajipen that very costulate Hehastrpcans have a union 

 between opposing costse by their spinulose growths, but it is a rare 

 and not invariable occurrence. The growth of the two genera is much 

 the same ; but the presence of exotheca extending beyond the costse 

 and between the corallites in Heliastrcea is a remarkable distinction, 

 and decides the comparatively symmetrical shape of the Heliastraean 

 calices. The genus Astrcea appeal's at first sight to be allied to 

 Phymastrcea ; but a careful study of its structure indicates that its 

 junction-processes are synapticula. 



The bushy forms which increase by gemmation from the external 

 wall below the calice, and which have a more or less complete 

 epitheca, and belong to the genus Cladocora, cannot be associa- 

 ted with Fhymastrau, for when junction of corallites does occur 

 in them it is through the epithecal bands which exist here and there, 

 and not by means of mural structures. 



In classification it is therefore requisite to leave the genus Phy- 

 mastrcea where MM. Milne-Edwards and Jules Haime placed it, 

 between Heliastrcea and the genera with entirely soldered or united 

 walls. 



VIII. The Affinities with Extinct Genera. 



Some of the early Secondary corals have a superficial resemblance 

 to Phymastrcea, especially the species of Elysastrcea described from 

 the Infra-Lias of the Sutton Stone and Brocastle in South Wales. 

 The resemblance is with the species described by MM. Milne- 

 Edwards and Jules Haime ; and the figures given by me in the 

 ' Monograph of the British Fossil Corals,' second series, part iv. 

 no. 1, Palseontog. Soc. 1867, plate vi. figs. 5-13, especially figure 

 10, are very suggestive. But the complete epitheca does not sur- 

 round junction-processes in Elysastrcea ; they do not exist. In the 

 genera more or less allied to Cladocora, and which are found fossil, 

 there are no junction-processes. The genus really stands alone in 

 its characteristic method of corallite union. 



