260 CWLEXTERATA. 



Sub Order III. MADREPORARIA. This group, the richest in species of 

 any, is characterized by the great development of the skeleton. Theca, 

 septa, and usually columella and synapticuli are present, and frequently 

 costaB as well. Solitary forms are few. Usually they form colonies, fre- 

 quently of thousands of individuals, bound together by a coenenchym 

 extending from polyp to polyp over the surface of the coral. A colony 



FIG. 214. Fio. 215. 



FIG. 214. Astrmigia danae* ; five polyps in various stages of expansion. 

 FIG. 215. Coeloria arabica. (After Klunzinger.) 



FIG. 216. FIG. 217. 



TIG. 216. Cladocora ccespitosa. (After Heider.) Relations of coral and flesh. 

 FIG. 217. Favia cavernosa. (After Klunzinger.) 



arises from a single animal by continued fission or budding. When the 

 division is not complete the animals may form long series with numerous 

 mouths but with the other parts united, the result being that the surface 

 of the coral is marked by long winding grooves incompletely separated 

 theca with sclerosepta, as in the brain corals (fig. 215). 



Since but little is known of the soft parts, the classification of the Mad- 

 reporaria is based upon the coral. Three sections of the sub order are recog- 

 nized. (1) APOROSA, with compact skeleton. Some, like Caryophyllia 



