1 66 



CORALS 



of the coralliim and even the size of the perforations remain 

 remarkably constant. It is one of the easiest corals to 

 recognise and name. 



Adeona. — Specimens of the exotic genus Adeona, found 

 in shallow water off the coast of Australia, Africa, and in 

 the South Seas, attain to the largest size of any of the 

 coral-forming Polyzoa. They consist of thick erect fronds 

 attached by a short flexible stalk to rocks, and they are 

 perforated by a number of round fenestra larger and more 

 scattered than in Retepora. 



Some very large fronds of this genus, measuring two feet 



in height and nearly 

 W*^^ ■ ♦ S ""^^ % '»~V» ;>*''''•■*■ cis much in diameter, 

 r**> ***l\f%'f''H^^ ♦ J;H^ ♦ l^a^'e ^e^" found, and, 

 I *k' # V«^^ 'i^^sW-'-r •^'irST^ as their substance is 



hard, calcareous, and 

 of considerable thick- 

 ness, they possess a 

 thoroughh" coral-like 

 aspect. 



At first sight 

 x\deona might be 

 considered to be a 

 large coarse species of 

 Retepora, but a de- 

 tailed examination of 

 the zooecia shows that 

 it is only remotely related to that genus. Among other 

 points of difference that may be observed is the presence 

 in Adeona of a second large aperture situated a little dis- 

 tance behind the orifice and frequently connected with it 

 by a shallow groove (Fig. 78). This second aperture is 

 smaller than the main aperture but distinctly larger than 

 the pores which decorate the sides of the zooecia. 



Closely related to Adeona is the genus Adeonella, which 

 forms masses of variously branched or ramified coral 

 substance sometimes attaining considerable dimensions. 

 The stem in this genus is not flexible as in Adeona, but the 

 colony is usually attached to some flexible support. 



Fig. 78. — Adeona. Surface view of a part 

 of a colony. : : 20 diams. 



