GENERA OF FAVOSITID^. 103 



Bill., both of which are, in my opinion, unmistakably con- 

 generic with the type-species, T. Davidsoni, E. and H., and 

 were so regarded by their respective founders. The investi- 

 gation of thin sections of these two species has led me to 

 entirely coincide in all points of substantial importance with 

 the account given of the genus by Dr Rominger, who unites 

 it with Dendropora, Mich. (Foss. Corals of Michigan, p. 60, 

 1877). It becomes quite clear, then, that there is no real 

 affinity between Trachypora, E. and H., and Seriatopora, 

 Lam. Not only is the columella of the latter genus totally 

 wanting in the former, but thin sections place it beyond a 

 doubt that there exists in Trachypora absolutely nothing of 

 the nature of a ccEuenchyina. It is true that the apertures 

 of the calices are widely removed from one another, and 

 that the dense calcareous tissue which separates them is 

 superficially sculptured in various ways ; but tangential sec- 

 tions (such as fig. 3 c, PI. V.) show that the appearance thus 

 produced — and mistaken, very naturally, by Milne- Edwards 

 and Haime as indicating the presence of an abundant ccenen- 

 chyma — is really due to quite a different cause. In reality 

 there is no ccenenchyma at all, and the essentially polygonal 

 corallites are in close contact by their walls throughout. The 

 wide interspaces which separate the openings of the calices 

 are truly formed by the extraordinary thickening of the walls 

 caused by the deposition of numerous concentric layers of 

 sclerenchyma in the interior of the tubes. The actual struc- 

 ture is, therefore, precisely that of Pachypora, Lindst., and 

 Striatopora, Hall, so far as this point is concerned — with the 

 difference, that the thickening of the immediate periphery 

 of the calices is carried to a much more extreme extent, 

 and that the free surface separating the openings of the 

 calices exhibits the peculiarity of being ornamented with 

 grooves or rido-es. This last-mentioned feature is, indeed, 

 the only definite character by which such species of the 

 genus as T. ornata, Rom., can be separated from Pachy- 

 p07'a, while other species (such as T. Davidsoni, E. and H., 



