86 



CORALS 



two directive septa there are four other hirge septa alter- 

 nating with six smaller ones. The colour of living colonies of 

 Pocillopora is usually green, sometimes " a most brilliant dark 

 green " (Gardiner). Other colonies are colourless or pink. 



Stylophora. — The genus Stylophora (Fig. 36) is not an 

 uncommon coral on the reefs of the Indian and Pacific Oceans, 

 and calls for a few words of comment, because, in some 

 respects, it has a superficial resemblance to varieties of the 

 Hydrozoan genus Stylaster (p. 153). 



As the name suggests, the most characteristic feature it 

 exhibits is the prominent pillar-like columella 

 (Fig. 37), which stands up in the centre of the 

 calyx, and as this feature is combined with 

 that of narrow and usually rather thick septa 

 the calyx has some resemblance to a pore 

 cycle of one of the Stylasterina. A critical 

 examination of a calyx shows, however, 

 that the spaces between the septa are not 

 pierced by dactylopores and that the six 

 thick primary septa are supplemented by 

 six thinner rudimentary ones. 



Stylophora is undoubtedly a Madre- 

 porarian coral, but the authorities are not 

 agreed as to its exact systematic position 

 and generally place it with Madracis in a 

 separate family — the Stylophoridae ; but it 

 agrees so closely in many important char- 

 acters with Seriatopora that there seems to be no sufficient 

 reason for excluding it from the family Seriatoporidae. 



The form of the corallum is usually arborescent, the 

 branches ending in thick blunt points, but sometimes it is 

 palmate or encrusting. The substance is hard and compact 

 except in the ax-is of the larger branches, where it becomes 

 porous, and the ends of the growing points, where it is per- 

 forated by calicular pores. 



The small calices are separated by a considerable amount 

 of coenenchym, which is adorned with a great number of 

 small blunt tubercles giving it a granular appearance. In 

 some specimens these tubercles fuse to form ridges. The 



Fig. 36.— Stylo- 

 phora. The ter- 

 minal branch of a 

 colony from the 

 Indian Ocean, x 2 

 diams. 



