194 ^- I' Robinson, 



tabellae form. Within the mound formed of tabellae, there is a 

 plate corresponding in direction to the cardinal and counter 

 septa. It is derived from the counter septum. This axial plate 

 is usually separated from the counter septum later in the life 

 of the individual, but sometimes a connection is preserved until 

 adult conditions are reached. Other lamellae develop correspond- 

 ing to the major septa, and still others arise independently. The 

 cross-section of a columella of this sort gives the pattern of a 



Fig. 7. Lonsdaleia. Longitudinal section of a single corallum, showing 

 tabulae, tabellae, columella, and dissepiments. (After Smith.) 



cobweb, which is a characteristic of this and related genera. The 

 presence of the continuation of the counter septum as an axial 

 plate in the columella and its evident influence upon columellar 

 development place this form in the group of parietal columellas. 

 Accordingly, the ontogenetic history of a coral individual is 

 summarized by Smith as follows : 



"la. The epithecal ring [basal plate] is laid down. 



"lb. The earliest septa appear attached directly to the 

 epitheca. 



"2a. The counter septum grows into the middle of the 

 corallites. 



"2b. The dissepiments appear as a narrow peripheral zone, 

 and may, even at this stage, separate the septa from the epitheca. 



"3. During this third stage the septa are prolonged into the 

 middle of the corallite and the tabulae bending distally around 

 the inner or 'axial* edges thus form the beginning of the central 

 column. Truncation of the inner edges of these long septa takes 

 place, and gives rise to* the first septal lamellae. * * ' * 



