70 CORALS AND CORAL ISLANDS. 



as to go by the popular name of " white coral," and to be some- 

 times polished for beads and other such ornamental purposes. 



Figure 2 is a branch of a beautiful little coral called Sty- 

 laster erubescens Pourt., and 3, a portion of the same enlarged. 

 It has the firmness, and something of the habit of an Oculina, 

 but is rather like a miniature Oculina, its calicles never exceed- 

 ing: a twentieth of an inch in breadth. There are a, number of 

 genera in this Stylaster family, the Stylasteridce, and the corals 

 are among the most delicate of species. 



Figure 4, in the same cut, represents a portion of a branch of 

 the Stylophora Dance E. and H. The corals of the genus are 

 remarkable for their small, crowded calicles, and for the very 

 distinct six-rayed star in each calicle (as shown magnified in 

 figure 5), and usually have a prominent point or columella at 

 the centre of the star. The polyp of a Feejee species, S. 

 mordax, is represented in figure 6. The name of the family, 

 Stylophoridce (signifying style-bearer), alludes to this colu- 

 mella. The corals grow in regular hemispherical clumps con- 

 sistino- of flattened or rounded branches, and are sometimes a 

 foot or more across. 



In another family under this tribe, the Pocilliporidw, very 

 common in coral-reef seas, the cells of the corallum are always 

 very small and crowded, as shown in figure 7. The corals are 

 branching, and in Pocillipora, the surface is often irregular and 

 warty, the little prominences, like the rest, being covered with 

 polyp cells ; while in Seriatopora, the branches are slender, 

 even, and pointed. The corallum in both is very firm and sol- 

 id. In the larger part of them the number of tentacles is only 

 twelve, and formerly they were referred on this account to the 

 Madrepore tribe ; a few have as many as twenty-four tenta- 

 cles. 



The Pocilliporag form hemispherical clumps like the Stylo- 



