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 Astreea 
The star-corals. The corals of this genus are hemispherical 
masses covered with small star-shaped pits, or corallites. Although 
the diameter of an astreea-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 acommon stomach. 
D. cerebriformis. 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.) 
