58 CORALS 



wiiilc those of the third and subsequent orders are very 

 small, and only to be found in the upper part of the 

 calyx. 



The differences between the three genera are not of very 

 great importance, and it may be that when some one has the 

 courage to revise the system on which the genera of these 

 corals is based thev will be amalgamated. In Eusmilia, 



Fig. 21. — Euphyllia, East Indies. | nat. size. The line called the " Edge-zone " 

 can be distinctly seen about I inch l)elow the rim of each calyx. 



according to the system in vogue, there is a spongy columella 

 at the bottom of a deep fossa, in Mussa it is rudmientary, 

 and in Euphyllia it is absent. Mussa differs from the other 

 two in having widely separated spines on the theca and 

 dentate septa, and also in having the septa very much more 

 exsert. Apart from the difference as regards the columella, 

 a very variable character on which to base a generic dis- 

 tinction, Eusmilia and Euphylha are almost identical. It 

 has been the custom, however, to refer specimens from the 



