CORALS AND CORAL MALy'ERS. 43 



page 37, illustrates one section of this family, that in which each 

 branch of the corallum is made by a single' polyp, and branch- 

 ing is by furcation through spontaneous fission. In other 

 related genera, as Mussa, the polyps sometimes have a diameter 

 of two inches, being as large as ordinary Actiniae. 



ASTK/KA PALLIDA, D 



The Astrcea pallida is a good representative of the massive 

 Astraeas. The colour of the polyps in this species is quite 

 pale, the disks being bluish-gray, and the tentacles whitish. In 

 others, the tentacles are emerald-green, or deep purple, or of 

 other shades. 



Another range of forms is represented by the following 

 figure of one of the Meandrine corals, already referred to as 

 often called " Brain coral.'' In the figure, the coral is reduced 

 one-half lineally. The difference betw^een its mode of for- 

 mation and that of an Astraja has been stated on page 38. 

 This species is common at the Bermudas, where it grows to a 

 diameter of three feet. It is also found in the West Indies. 

 The ridges in this species are double, and hence the name 

 Diploria, from the Greek for double. A common large West 

 India species of Brain coral is called Meandrina labyri7ithica. 



