TRIBE III. MADREPORACEA. 551 



These zoophytes are confined to the coral-reef seas. They occur 

 in the West Indies, as well as in the Pacific and Indian Oceans; but 

 the branched species of the former region are generally remarkable for 

 a less durable texture. 



The genus Porites, as restricted by Lamarck, contained various 

 unallied species, characterized by their minute cells. Blainville 

 separated from it the genera Sideropora, Alveopora, and Heliopora, 

 which a farther study of the animals has sustained ; and to these, the 

 genus Manopora is added in this work. 



The Porites pyriformis of Lonsdale and other allied species, are 

 related to the Helioporse, with which they were arranged by Blainville. 



The genus Porites, as here received, contains the Madrepora Porites* 

 of Linnaeus, Pallas, and other early authors, from which the name was 

 derived. 



This genus graduates into Alveopora and Manopora ; yet the species 

 of the latter groups are distinct, in their deeper and delicately stellate 

 cells, which in the Manopora? are not contiguous. When the cells 

 of the Manoporae are quite minute, the internal texture of the corallum 

 approximates to that of the Porites, both in its general porous cha- 

 racter, and the difficulty of tracing the cells through it. The P. as- 

 traeoides has nearly the short twelve-rayed star and columella of some 

 Pocilloporse, though wholly different from them in the texture of the 

 corallum. 



Arrangement of the Species. 



A. Ramose, branches often compressed, but not plicate. 



I. Cells excavate. 



*1. P. mordax. *5. P. furcata. 

 *2. P. compressa. 6. P. recta. 



*3. P. clavaria. *7. P. divaricata. 

 *4. P. flexuosa. 



II. Cells superficial or none. 



*8. P. nigrescens. *10. P. levis. 



*9. P. palmata. *11. P. cylindrica. 



B. Branches plicate. 

 *12. P. contigua. 



* The Porites clavaria of Lamarck. 



