148 MARINE INVERTEBRATES 



and the beautiful sea-pens are both highly colored and phos 

 phorescent. Owing to the fact that these brilliantly colored 

 polyps were mistaken for blossoms, the recognition of their true 

 character was long delayed, they having been ranked as vege- 

 tables until comparatively recent times. 



With few exceptions, corals do not grow in water below the 

 temperature of 68, hence they are inhabitants of tropical and 

 subtropical waters. The Florida Keys are coral reefs, and the 

 species described below are to be found there. 



GENUS Oculina 



Arborescent ; corallites arranged somewhat spirally on branches 

 and widely separated; branches compact between corallites. 

 Each bud is for a time at the apex of the branch, but finally be- 

 comes lateral, and then gives off another bud from its upper sur- 

 face, and so the stem lengthens. (Plate XLIV.) 



GENUS Astrcea 



The star-corals. The corals of this genus are hemispherical 

 masses covered with small star-shaped pits, or corallites. Although 

 the diameter of an astrsea-dome may be twelve feet or more, 

 it has only one half or three quarters of an inch of living coral 

 on its surface, the rest being solid matter left behind as the 

 polyps rose in growth. The colony increases by self-division. 

 The septa meet in the center of the corallite, making star-like 

 pits ; the surface is comparatively smooth. (Plate XLIV.) 



GENERA Meandrina, Diploria 



Corallum massive, hemispherical in shape, with furrows running 

 in irregular lines over the whole surface. The peculiar serpentine 

 form of the corallite is produced by the animal growing in one 

 direction, fission being incomplete, and new mouths being succes- 

 sively opened until a line of them extends along a common stomach. 



Z>. cerebrifomiis. This species is commonly known as brain-coral 

 or brain-stone. The hemispherical shape, together with the peculiar 

 serpentine corallites, makes its resemblance to the human brain very 

 noticeable and the name unusually appropriate. This species, when 

 living, is bright yellow. (Plate XLV.) 



