SUBDIVISIONS OF ACTINOID POLYPS. 



65 



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 re- 

 duced one-half lineally. The difference between its mode of 

 formation and that of an Astraea, has been stated on page 59. 

 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, 



DIPLOMA CEREBKIFORMIS, E. AND H. 



from the Greek for double, A common large West India 

 species of Brain coral is called Meandrina labyrintliica. It is 

 readily distinguished from the Diploria by the ridges between 

 the furrows, these being simple and triangular. 



Still other forms of the Astraea tribe are foliaceous, or such 



as would result if the growing margin of an Astraea, or of a 



Meandrina, were to spread out into folia instead of thickening 



upward in the ordinary way. The groups of gracefully curv- 



5 



