GENERA OF FAVOSITID^E. 109 



with that of the stems, two-thirds or three-fourths of a line in 

 their long diameter, and about half a line across, surrounded 

 wholly or for their lower two-thirds by a slightly-elevated rim, 

 which is sometimes marked with radiating striae. The thick- 

 ened margins of the calices separate contiguous apertures to a 

 width about equal to the long diameter of the latter, and form 

 by their union dense interstitial spaces, which are marked by 

 slightly flexuous broken striae. Septa apparently obsolete. 

 Tabulae few in number or seemingly absent. Mural pores not 

 recognised. 



Obs. The external characters of this species, as given in the 

 above diagnosis (PI. V., figs. 4 and 4 a), sufficiently separate it 

 from all the known forms belonging to the genus. The inter- 

 nal structure, however, presents various points which are as 

 yet not sufficiently elucidated, the remarkable density of the 

 corallum rendering the preparation of satisfactory microscopic 

 sections a matter of exceptional difficulty. In most of its 

 structural features, T. elegantula, Bill., does not differ greatly 

 from such forms as T. ornata, Rom., with which it is undoubt- 

 edly congeneric ; but the thickening of the corallites by a 

 secondary deposit of sclerenchyma is carried in the present 

 form to an extreme extent. This is seen particularly in the 

 fact (as shown both by transverse and vertical sections) that the 

 actual walls of the corallites are more or less obliterated (PI. 

 V., figs. 4 b and 4 c], and are not present as distinct partitions 

 definitely circumscribing the individual tubes. In the centre of 

 the stem, where the thickening has not been excessive, the 

 walls are still distinctly recognisable (PI. V., fig. 4 b} ; but as 

 the thickening increases in approaching the surface, the definite 

 lines indicating the proper walls disappear, and the boundaries 

 of contiguous corallites are now only marked by an obscure but 

 still quite unmistakable band of thickened tissue, occupying 

 the place of the wall (PI. V., fig. 4 c). On the surface, the 

 polygonal margins of the calices which are quite recognisable 

 in T. ornata, as ridges surrounding the actual orifices of the 

 tubes at some little distance are no longer to be detected at 



