THE GRAPTOLITES AND CORALS 



299 



corresponds to the convex curve of the horn (Fig. 89, b). 

 The sides and floor of the calyx bear a radiating series of 

 ridges, the septa, which are the most distinctive character 

 of corals in general. In this species they are over sixty 

 in number and arranged in an alternation of two series. 

 One series, the major septa (or entosepta), extend from the 

 margin of the calyx to the centre of its floor. The 



H 



FIG. 89. ZAPHRENTIS KONINCKI, MILNE-EDWARDS AND HAIME. 



Diagrams of vertical and transverse sections. (After Carruthers, simplified. ) 

 a. Vertical section. (X2.) Cardinal and counter septa dotted. 

 f, fossula. b, Transverse section. ( X 5.) H, Cardinal ; CS, counter ; 

 A, alar septa; a-g, metasepta, lettered in order of development. The 

 short unlettered septa are minor septa. 



alternate minor septa (or exosepta] are thinner, less 

 prominent, and confined to the calyx sides. Although 

 the septa are, in a general way, radial, the presence of 

 the fossula makes the whole calyx very distinctly bilateral, 

 and there cannot be said to be more than an approxima- 

 tion to radial symmetry. The major septum which 

 corresponds to the middle line of the fossula is shorter 



