428 ZOOPHYTES. 



TRIBE III. MADREPORACEA. 



Actinaria tentaculis duodecim (rarissime pluribus] uniseriatis, alternis 

 inter dum minoribus: gernmipara; gemmatione inferior e: coralligena; 

 corallis calcareis, cellis 6-12 radiatis aut lamettis obsoletis, superficie 

 interstitiali non lamello-striata. 



Actinaria with the tentacles 12 in number (rarely more), in a single 

 series, the alternate sometimes smaller: gemtniparous; gemmation 

 inferior: coralligenous ; coralla calcareous, with the rays of the 

 cells 6 to 12 in number or obsolete, interstitial surface not striated 

 with the prolonged lamellae of the cells. 



The polyp of the Madrepore tribe is a simple star-shaped animal of 

 twelve rays, presenting generally bright green, red, or umber tints. 

 The rays or tentacles are at times nearly obsolete, or are reduced to 

 rounded crenations of the circular disk, and in species of this cha- 

 racter, lilac, yellow, and green colours of different shades have been 

 observed. 



The corallum is at once recognised by the few rays to the cells, the 

 number being twelve or less, and sometimes the whole are obsolete. 



Among the forms of these zoophytes there is nearly every variety 

 that occurs in the Actinaria; but the glomerate are never as neatly 

 regular as among the Astrseas, while the ramose forms are singularly 

 varied and beautiful. Segregate ramose forms, like those of the Cary- 

 ophylliaB, are never met with ; and only among the fossil Favositidse, 

 do we find coralla consisting of separable columns a structure arising 

 from the fact that the polyps (as in the Columnarise) are united late- 

 rally only by their outer non-secreting integuments. 



This tribe includes three families, as already explained : the Ma- 

 dreporidBe, the Favositidse, and the Poritidse. 



The following table contains the received genera of this tribe, and 

 exhibits their relations to the corresponding genera adopted by the 

 distinguished authors whose names are placed above the several 

 columns. 



