136 ME. H. M. BERNARD ON RECENT PORITID^. 



where in this latter. That such may indeed have been the case we 

 know from the fact that species of Alveopora occur in which the 

 lateral expansion of the colony is so pronounced that the usually 

 conspicuous epitheca becomes little more than a film protecting 

 the coral from the substratum, although there are here no exsert 

 septa out of which to form an internal theca in the manner 

 shown in the diagram. The same can also be shown in the 

 genus Croniastrcea, which multiplies by what is called fissiparity. 

 Two prominent septa mark off" the skeleton of the bud *. The 

 skeleton of the colony is here again septate, and the epitheca is 

 flattened out by colony-formation, that is, not in the way shown 

 in the diagram. 



This point was not evident in my former paper, even though 

 I left it undecided whether Porites was to be regarded as related 

 to Madreporidse or to Alveopora. It was quite clear that the 

 epitheca of Forites was flattened out, and that the theca was 

 therefore internal (fig. 1, D); but I saw only two ways in which 

 this could have occurred, and in both the epitheca was slowly 

 replaced in an essentially similar way, viz., by the rising up of an 

 internal theca, formed by the septa becoming more and more 

 exsert. The theca of Forites might, I thought, be either a 

 secondary modification of that of the Madreporidse by the per- 

 foration of the lamellate septa, or an independent development 

 from a form like Alveopora with horizontal spine-like septa. In 

 this latter case, as the epitheca flattened out, the spines would 

 become vertical and form the vertical " trabeculse " of Forites. I 

 now see, however, that the epitheca might be flattened out in the 

 process of colony-formation, when the skeleton of the bud is 

 marked oflT by the meeting of septa which cut off a portion of the 

 parent calicle. 



We have, then, three apparently possible origins of Forites. 

 Of these we niay, I think, safely dismiss this last suppos-ition, 

 viz., that the flattening out of the epitheca was due to the rapid 

 lateral budding of some fiissiparous coral. Such an origin would 

 give us no explanation of the radial series of " trabeculse " or of 

 the thick intervening walls. 



Returning, then, to the main alternatives, we have to decide 



* This method of budding may be compared with that described in a 

 former paper (Journ. Linn. Soc, Zool. vol. xxvi. p. 495, pi. 33. fig. 10) as that 

 of an Astrseid ! 



