38 TABULATE CORALS. 



those with a hemispherical or globose corallum, have the lower 

 surface covered with a thinner or thicker, concentrically-striated 

 epitheca, while the calices are placed upon the upper surface. 

 The ramose species possess no true epitheca. 



In the massive and more typical species the corallum is fixed 

 by a portion of its base to some foreign body ; and from this 

 point the long and prismatic corallites radiate to the surface, 

 those in the centre of the mass being nearly vertical in direc- 

 tion, while those towards the margins become more and more 

 inclined, till they become nearly or quite parallel with the 

 lower surface. New corallites are intercalated by gemmation, 

 as the tubes proceed towards the surface. In the ramose 

 species, the corallites are vertical in the centre of the branches, 

 and gradually bend outwards, in a radiating manner, till they 

 open on the circumference in a direction more or less nearly 

 rectangular to the surface. 



The corallites are typically markedly prismatic, usually pen- 

 tagonal or hexagonal, but they may become more or less cylin- 

 drical in whole or in part. The tubes are never united by the 

 actual fusion of their walls, though always in contact, and 

 their walls are typically of no great thickness. In some forms, 

 however, which have been commonly referred to Favosites, but 

 which will here be placed under the allied genus Pachypora, 

 Lindstrom, the walls are extraordinarily thickened by a second- 

 ary deposit of sclerenchyma, and we find an approximation to 

 this in some species which must still be left in Favosites proper. 

 In all the species of Favosites, further, the visceral chambers of 

 contiguous corallites are placed in communication by means of 

 a series of circular apertures or " mural pores." These fora- 

 mina are usually arranged in a regular manner ; and though 

 this arrangement is not absolutely constant for, perhaps, any 

 given species, still it is approximately uniform in its character, 

 and thus affords a useful guide in specific diagnosis. Thus, in 

 certain species {e.g., F. turbinata. Bill.) the pores are typically 

 uniserial — that is to say, each of the flat faces of the prismatic 

 corallites carries a single row of these apertures. In another 



