78 CORALS AND CORAL ISLANDS. 
In the genus Porites, the corals are frequently branching, as. 
in the Porites mordax D., sometimes more slenderly, but oftener 
less so, and at times massive and monticulose in form. An- 
other species of Porites is represented on the following page, 
with one of the branches fully expanded, but the others in 
outline; a polyp, much enlarged, having twelve tentacles as 

POLYP OF PORITES LEVIS. 
in the Madrepore, is shown in the following figure. |The cells 
of the corallum are superficial, and hence the name of the 
species, Porites levis. 
Another form, different in the size and character of its 
polyps, is exemplified in the genus Goniopora. In the species 
figured on p. 52, the color of the projecting polyps was lilac 
or pale purple, and the number of tentacles eighteen to twenty- 
four, yet all were in a single series. The columns grow to a 
height of two feet or more, with only the summits for two or 
three inches alive. The dead portion is usually encrusted with 
nullipores, sponges, serpule and various shells, which protect 
the very porous corallum within from wear and solution by 
the moving waters. 
3. CYATHOPHYLLOIDS, 07 RuGosa. TETRACORALLA. 
It is not necessary to dwell here at length upon the an- 
cient Cyathophylloids. The corals have a close resemblance 
to those of the Astreea tribe in general aspect, varieties of form, 
and range of size; the methods of multiplication by buds were 
the same that are now known in the Oculina tribe. Some 
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