GENERA OF FA VOSITID^. 



149 



epitheca, marked with concentric and radiating strise. All my 

 specimens show a distinct cicatrix of attachment, the foreign 

 body upon which the coral grew being in one instance unques- 

 tionably the column of a Crinoid (iig. 22, d). I can also detect 

 no traces of perforations nor of radiciform prolongations of the 

 epitheca. The upper surface (fig. 22, c) shows the apertures 

 of the polygonal, irregularly-sized corallites. Tangential sec- 

 tions, taken just below the upper surface (PI. VIII., fig. i a), 

 cut across the corallites at right angles, and show that the 

 polygonal tubes are surrounded by thick walls, those of con- 

 tiguous corallites remaining so far distinct as to be always 

 ' separated from one another by a marked and definite line of 

 demarcation. The same feature is shown by sections which 

 cut the corallites longitudinally (PI. VIII., figs, i and i b). 

 Both these kinds of sec- 

 tions exhibit, further, the 

 well -developed but irreg- 

 ularly-distributed " m ural 

 - pores," together with cer- 

 tain o ther openings of a 

 seemingly different nature, 

 the structure of which I 

 shall endeavour to eluci- 

 date by the help of the an- 

 nexed diagram. Remem- 

 bering that the mural pores 

 are apertures which pass 

 throuofh the walls of the 

 corallites from side to side, 

 it is easy to see how and 

 under what forms they may 

 present themselves in thin 

 sections of the corallum of 

 any of the FavositidcB. In 



transverse sections (fig. 23, a and c) the pores are usually 

 not to be detected, or only here and there, and they present 



Pig. 23. Semi-diagrammatic representations of 



sections of the corallum of Favosites and Pleuro- 

 dictyum, showing "mural pores" and "intra- 

 mural canals," the former shaded black, the 

 latter left unshaded. A and B, Transverse and 

 vertical sections of Favosites, showing mural 

 pores only; c and D, Transverse and vertical 

 sections of Pleurodictynin, showing mural pores 

 and intramural canals. 



