52 J. E. DUERDEN. 



and are inclined towards and fused in a successive manner with 

 the dorsal older septa. 



2. Alar fossulae indicate with an incomplete stage in the radial 

 development of septa, and similar stages are passed through in the 

 ontogeny of other rugose corals in which the mature calice attains 

 more nearly radial symmetry. 



3. The cardinal or ventral-directive fossula where best devel- 

 oped is formed by two distinct structural elements : (a) a group 

 of incompletely developed septa on each side of the ventral direc- 

 tive or cardinal septum, and (fy a ventral directive or cardinal 

 septum smaller than the other septa of the first cycle. 



4. The two ventral groups of incompletely developed septa 

 have a significance similar to that of the alar fossulae, that is, 

 they represent a developmental stage. 



5. The smaller cardinal septum was probably correlated with 

 the presence in the rugose polyp of a ventral siphonoglyph or 

 gonidial groove in the stomodaeum, like that which occurs in the 

 living Zoantheae. 



6. In the most radially developed species the simple cardinal 

 fossula is' represented by only the shortened directive septum. 



7. Like modern corals and ccelenterates generally all the Ru- 

 gosa exhibit bilateral symmetry during their development, and 

 as they approach maturity they become more or less radial. 



8. The bilaterality and radiality of tetracorallids and hexa- 

 corallids are of very different origin and character, and along with 

 other characteristics of the two groups do not imply any rela- 

 tionship beyond the protoseptal stage. 



RHODES UNIVERSITY COLLEGE, 



GRAHAMSTOWN, CAPE COLONY. 



