MADREPORARIAN CORALS 



4T 



broken off. The outer wall does not show any trace of 

 costae, but there is a series of more or less well-marked 

 transverse lines of growth. The principal peculiarity of 

 the genus, however, is that the polyp is entirely restricted 

 to the inside of the calyx. It does not overflow, as in many 

 of the corals, so as to cover the whole or the upper part 



of the outside of the 



calyx with its soft 

 living flesh. As the 

 outer wall of the calyx 

 is thus wholly exposed 

 to the sea - water, it 

 frequently forms the 

 support of worm-tubes, 

 polyzoa, barnacles, 

 and foreign bodies of 

 various kinds. The 

 process of formation of 

 the wall of the calyx 

 in Flabellum appears 

 to be of a different 

 type from that in the 

 other Turbinoliidae, as 

 shown by the absence 

 of costae and the pre- 

 sence of foreign bodies, 

 and it is therefore 

 usually regarded as an 

 epitheca and not as a 

 true theca. 



In the younger 

 stages of its life the base comes to a blunt point, terminating 

 in a small disc for attachment to a shell or rock, but when it 

 has attained to a certain size this point is broken off sharply, 

 leaving an oval scar at the base in which the septa are exposed. 



After the coral has broken off its base of attachment 

 in this way, one or more pairs of wing-like processes may be 

 formed on the edges of the epitheca, or in some cases hollow 

 root-like tubes grow from the scar. 



Fig. 12. — Flabellum rubrum. The upper 

 figure shows the cavity of the calyx and the 

 septa. The lower figure is a side view showing 

 the lateral processes and the scar at the base. 

 Nat. size. 



