124 A NATUBALI8T IN CELEBES ch. vi 



ful and beautiful forms, being sometimes fan-shaped, some- 

 times considerably branched like a small bush or shrub, 

 sometimes multilobate like a number of blunt fingers 

 standing upon a swollen wrist. 



The Turbinarias are like the madrepores in general 

 structure, but they usually form thin plate-like coralla which 

 frequently become cup or saucer or plate-shaped. 



The Fungias are large solitary forms, sometimes nine 

 to ten inches across. Each is composed of a large fleshy 

 polype resting on an oval mushroom-shaped skeleton. 



The remaining Zoantharians are distinguished from 

 those corals just described by secreting a skeleton which is 

 never perforated throughout by canals and pores. To this 

 order belongs the enormous family of the star corals, As- 

 trseidse, most of which form large solid stone-like masses 

 marked by a perfect system of star-like thecse. It also in- 

 cludes the well-known brain corals {Mceandrinas),i\xe, mussas, 

 galaceas, and many others. 



The Pocilloporas and Seriatoporas, which must be in- 

 cluded in the order Imperforata, although their exact 

 zoological position has not yet been accurately determined, 

 form branched bush or shrub-like structures not unlike some 

 of the madrepores in form, but their surface is smoother 

 and the thecse not nearly so conspicuous as they are in 

 those corals. 



Besides the Zoantharia two other classes of animals 

 form complicated and massive calcareous skeletons which 

 help to build up the coral reefs in tropical seas. Among 

 the so-called Alcyonaria two genera alone in tropical seas 

 form solid calcareous skeletons. The first of these is the 

 blue coral (Heliopora ccerulea), which forms thick folds and 

 plates of spongy limestone of a pale blue colour, and the 

 organ-pipe coral (Tubipora musica), which builds up huge 

 red clumps of small pipes traversing layer upon layer of 



