312 



ZOANTHARIA. 



being thus placed in direct communication ; but the perforations 

 are not irregular, and are restricted to definite, circular or oval 

 apertures known as " mural pores." There is no true coenenchyma ; 

 and the condition of the septa is extremely variable, these structures 

 being sometimes obsolete, sometimes in the form of marginal ridges, 

 and most commonly in the form of vertically disposed rows of 

 spinules. Tabulae are usually well developed and complete, but 



ISPS 



Fig. 194. — Thin sections of Favositoid Corals, showing the phenomena presented by the mural 

 pores, a, Tangential section of Favosites sp., from the Devonian of Queensland, enlarged six 

 times, a', Vertical section of the same similarly enlarged ; in two of the tubes the section 

 traverses the centre of the visceral chambers, but in one it corresponds in part with the wall of 

 the corallite. b and b', Tangential and vertical sections of Alveolites Labechei, E. & H., from 

 the Wenlock Limestone of Ironbridge, enlarged ten times. [The septal thorns which characterise 

 this species, as also A. Battersbyi, E. & H., are mostly omitted in the drawing.] c and c', Tan- 

 gential and vertical sections of Pachypora sp. , from the Corniferous Limestone of the Falls of the 

 Ohio, enlarged ten times. In all the figures the letter/ indicates the mural pores. (Original.) 



they are sometimes imperfect. The corallum increases by the form 

 of budding which Waagen has denned as " inter-mural gemmation " 

 (see p. 254). 



The family of the Favositidcz is obviously allied to that of the 

 Po?'itidce, from which it is separated principally by the fact that the 

 walls of adjacent corallites are not undistinguishably fused (though 

 they may appear to be so in specimens in bad preservation), while 

 the perforations in the walls are in the form of more or less definite 



