The Relationship of the Tetracoralia to the Hexacoralla. 193 



adult. In the case of .lulopliyllum, while there is a stage in 

 which the septal ends are involved in the columella, they are 

 always clearly distinct from it. Likewise in Cyathaxonia (Fig. 

 6), although the earliest stage of the columella must actually rest 

 upon the central junction of the septa, these do not become 

 involved but rather are excluded very quickly from the central 

 area by the growing columella. In Lophophyllum, on the con- 

 trary, from the earliest stage until old age, the orientation, shape, 

 and size of the columella are noticeably affected by a septum. 

 In the case of parietal columellas which are actually crowded 

 septal ends or appendages of septa, the distinction from the 

 essential columella is so obvious that there is no danger of 

 confusion. 



Fig. 6. Longitudinal sections : a, Zaphrentis ; b, Lophophylluin : c, Cya- 

 thaxonia. Heavy black shows areas of secretion of calcium carbonate. 

 Nat. size. (After Carruthers.) 



The genus Aulophyllum is a fine example of the versatility of 

 columella variation. Not only do the size, shape, and compact- 

 ness of the columellas vary in different specimens, but they are 

 also extremely variable from time to time in the life of the same 

 individual. This shows a sensitiveness to minor changes in the 

 life processes which limits the value of columellar variation in 

 classifying the larger groups of corals. 



Lonsdaleia.- — The parietal columella of Lonsdaleia has been fig- 

 ured and described by Stanley Smith (1916). It is a large 

 central column such as is found in the Clisiophyllids generally. 

 It appears rather late in the life of the individual, when there 

 are about twenty major septa. At this time, either a group of 

 tabellee is formed or the tabulae are drawn up into a peak at the 

 center (see Fig, 7). As the development proceeds, the tabulae 

 are broken up altogether at the center and a large number of 



