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 repiesented 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 OP PORITES LEVI& 



in the Madreporee, 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, serpulae and various shells, which protect 

 the very porous co' allum within from wear and solution by 



the moving waters. 



II. CYATHOPHYLLOIDS. 



It is not necessary to dwell here at length upon the an- 

 cient Cyathophylloids. The corals have a close resemblance 

 to those of the Astraea 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 



