182 



FOSSIL ACTINOZOA. 



The number of the septa (when present at all) varies, but 

 there are never less than six of these structures, and however 

 great the number may be, a " hemmeral " arrangement of the 

 septa can be usually more or less clearly demonstrated in the 

 corallum of the Zoantharia sclerodermata. Hence the name 

 of Hexacoralla often applied to this group of corals. While 

 the rule among the Zoantharia sclerodermata is that the septa 

 are arranged in six systems (see fig. 70, A), and are, however 

 numerous, some multiple of six, there are cases in which no 

 such hexameral arrangement is demonstrable. 



Fig. fl.Caryophyllia (CyatMna) BowerbanU, from the Gault (Cretaceous). The left-hand 

 figure represents a specimen imperfect above, and enlarged, showing the tuberculated costse. 

 The right-hand figure is a magnified cross-section, showing the septa and pali. (After Milne- 

 Edwards and Haime.) 



As connected with the septa, we may also notice here the 

 structures which are known as "pali." These are " small 

 processes which exist between certain septa and the columella 

 (fig. 71). They generally arise from the base of the visceral 

 cavity, or close to it, and pass upwards, united by one edge 

 to the columella, and by the oth^r to the inner end or margin 

 of the septa. When there is no columella, they are adherent 



