SUBDIVISIONS OF ACTINOID POL YPS. 75 
dark blackish green or almost black color, while the polyps 
have the tentacles nearly colorless, and the disk has a circle 
of emerald green around the mouth. Dendrophyllia arborea is 
the name of a common species of this genus found in deep 

POLYP OF DENDROPHYLLIA NIGRESCENS. 
water in the Mediterranean ; it is equally large with the pre- 
ceding, and somewhat similar in its mode of branching, but 
a little stouter. It has also been found in the Atlantic about 
the Azores. Another common Mediterranean species is 
the D. cormgera. It is sparingly branched, and has very 
long and stout corallets, sometimes as long and large as the 
finger. 
The genus Gemmipora contains porous corals, of foliaceous, 
bowl-like, and massive forms, covered by prominent cylindrical, 
porous calicles, and having many short tentacles to the polyps, 
usually in a single circle. 
Here belongs also the large Porites family (Poritidz), the 
corals of which are very porous, and sometimes almost spongy, 
and whose polyp-cells are exceedingly shallow, and usually only 
imperfectly radiated. 
One of the genera in this family is Alveopora. It con- 
tains the lightest of known corals, the texture being exceeding- 
