ON THE BRITISH FOSSIL CORALS. 131 



The number of septa and the habit of growth of the two genera separate 

 them very widely ; and the propriety of connecting the last-named one with 

 the MUleporidse must be considered. 



There are four genera in the family of the Seriatoporidte : — Seriatopora, 

 Dendropora, JRhahdopora, Trachypora. 



The family is characterized by the continual growth of the lower parts of 

 the corallites and the rarity of tabulte. 



Seriatopora is a recent genus, and therefore those associated with it must 

 be carefully examined. 



Dendropora, Michelin, is clearly too closely allied to Bhahdopora to be 

 separated generically. 



Rhahdopora, formed for the Dendropora megastoma, M'Coy, by MM. MUne- 

 Edwards and Jules Haime, has only one species, the diagnosis of which is as 

 follows : — 



Rhahdopora megastoma, M'Coy, sp. — The corallum is branching. Branches 

 four-sided, starting from the stem at an angle of 70°, and very equal. Coe- 

 nenchyma granulated or subechinulated and obscurely striated. Calicos in 

 vertical series on each face of the branches. Septa (teeth) 12 in number and 

 subequal. 



It is impossible to separate this from Seriatopora, for the four-sided suture 

 of the branches is only a specific (if that) distinction. 



Trachypora appears to be an Alcyonarian. 



The distinction between PociUopora and Seriatopora is not generic, and 

 therefore these genera and Dendropora (for Dendropora and Rhahdopora 

 are equal, and the first name is the oldest) are absorbed in one. Oken'a 

 name Acropora (1815) may be used as the generic term : — Acropoea 

 {Seriatopora, Lamarck ; PociUopora, Lamarck ; Dendropora, Michelin ; Rhah~ 

 dopora, Ed. & Haime). 



All the species of the absorbed genera should take the generic name of 

 Acropora, and the family becomes that of the Acroporinaa. Thus the sharp 

 distinction between the recent and Palaeozoic forms is partly smoothed down, 

 and the old Dendroporre and Rhabdoporge were doubtless the ancestral 

 forms of the recent Acroporse. Ccenites cannot be associated with the 

 family. 



The family of the Thecidese is characterized by well-formed septa, which 

 are prolonged throughout the visceral chamber, well-developed tabulae, which 

 grow like dissepiments upon the sides of the septa, and these last do not 

 spring from the upper surface of the tabiilse, as in some Tabulata. The walls 

 are solid, compact, and united. 



The corals contained in the family are all Silurian forms, so far as is 

 known at present. 



Thecia, Ed. & Haime. It is a most remarkable fact that this genus, the 

 species of which have no true wall, but a dense ccenenchyma between septal 

 prolongations or costa?, should here give the family name. Tliecia Siuinder- 

 niana, Goldfuss, sp., has been called ^(7«nc?'a, Porites, Astreopora, and PaJceo- 

 pora by different authors, so that its classificatory position may well be a 

 matter of doubt. It is not in the least allied to Columnarife, which has soHd 

 walls, and which fulfils all the characteristics of the Thecidaj. 



In Thecia, Ed. & H., there is a long visceral cavity surrounded by a dense 

 tissue, as in Mtllepora, through which the septa, or rather the costa, run. 



What is the structure of Plasmopora and Propora but that of Thecia 

 slightly modified. The genus clearly must be associated with them amongst 

 the Milleporidip. 



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