ASTEOCCENI^ OF THE SFTTOX STOIfE. 103 



The walls of the corallites are united and fused together, and there 

 is no intermediate structure in the form of exotheca or coenenchyma. 

 The marldngs in the hard part, the original calcareous tissue of 

 the corallite, which denote the costae, cross the wall as in typical 

 Astrocoenice. 



The septa of full-grown corallites are twenty in number, and 

 there are ten which join the central, styloid, essential columella, and 

 ten much smaller which project but slightly into the calice : but some 

 of them may unite with the larger septa at no great distance from 

 the margin of the lumen. The larger septa in these perfect corallites 

 are without definite cyclical arrangement, and are nearly equal in 

 size. They are stout, straight, and slightly spinulose laterally, and 

 many have an enlargement midway between the margin and the 

 columella, but probably this is a result of fossilization. In some 

 corallites this thickening is universal, in others it occurs on some 

 septa only, and in many it is not seen. The smaller septa may unite 

 with the larger near the columella when gemmation is imminent, 

 and frequently no union is seen, in the largest corallites, between 

 any septa. Usually the small septa project very slightly inwards ; 

 and they do not invariably occur between the larger ones. 



Longitudinal sections show a close ornamentation of horizontal 

 ridges and grooves on the septal laminae (fig. 9). 



The path of the septa between the margin of the lumen of the 

 corallites and the columella is always distinct ; but the gradation 

 of the septa into costae is difficult of recognition in the section, and 

 principally because of the existence of radiating white markings 

 crossing the walls. 



It appears, under a low power, that the majority of the whiter 

 markings are in relation to septal commencements at the margin of 

 the lumen of a corallite, and that they are usually continued on the 

 walls in a line with the normal position of costse which correspond 

 with septa. 



But sometimes the markings are between the septa at the margin, 

 and do not correspond to costa?, and here and there the markings 

 are in continuation with the median line of a septum. Nevertheless 

 it may be said that the costoe are short, cover the walls, and inter- 

 digitate with those of the septa of the neighbouring coraUites. 

 There is no exotheca between them (fig. 6). 



The columella is circular in outline in the transverse sections of 

 corallites ; it is usually a third of the diameter of the lumen, and is 

 more when fossilization has added to the material of the coral. 

 Sometimes there is a ledge of endotheca, or stereoplasm, around the 

 columella, and it is evident that while in small calicos the structure 

 of the columella differs but slightly from that of a junction of septal 

 ends, in most it is a well-differentiated structure. A few calicos 

 have the columella slightly elongated in transverse section. In the 

 instances of gemmation the columella soon appears and is circular 

 in outline, while that of the parent is often deformed. 



In smaller corallites than those which have been described, the 

 septal number varies ; there may be seven or eight large septa in 



