MADREPORARIAN CORALS 99 



large number of calices, which usiiany project a httle from 

 the general surface, and between them there is a variable 

 amount of profusely perforated coenosteum which is not 

 marked with ccstal ridges. 



The surface of one of these large Turbinarias affords an 

 interesting study in variation. The student finds on the 

 same frond calices that vary in size from 0-5 mm. to i-o mm. ; 

 he finds that some calices project from the surface with 

 thick cup lips and others are almost flush with the surface, 

 and that in some parts of the corallum the calices are 

 crowded together and in others are separated by consider- 

 able areas of coenosteum. 



A similar excessive variation is also seen in the details 

 of structure of the calices. The number of septa rarely 

 exceeds twenty-two, but any number from seventeen to 

 twenty-two may be crowded in a full-grown calyx. The 

 septa are usually of approximately equal size, so that it is 

 impossible to recognise the directive septa or to distinguish 

 the primaries from the secondaries. The most remarkable 

 feature of the septal system, however, is that the number 

 of septa does not seem to bear any relation to the number 

 twelve, and it is this pecuKarity which renders the position 

 of the genus in the family Madreporidae a doubtful one. 

 A columella is usually present, but it is also very variable. 

 There are no pali. 



The pairs of mesenteries of Turbinaria correspond in 

 number with the septa. There are two pairs of directive 

 mesenteries arranged in a plane almost parallel with a radius 

 of the colony. The number of other pairs of mesenteries 

 varies and is not the same on the two sides of the directive 

 plane. 



According to Saville-Kent " the tentacles are numerous 

 and simply subulate," and the colour of some of the varieties 

 is rose-pink or yellow. 



It has been supposed that in an early stage of the develop- 

 ment of a Turbinaria colony there is an important difference 

 between this genus and Madrepora. It was suggested that 

 whereas in Madrepora the primary polyp and the calyx it 

 forms becomes the axial polyp on the sides of which the 



