238 CLASS IIL— ORDER III. 



expansion, as has been already observed, is stiff and 

 brittle ; its hardness is equal to that of many of the 

 Madrepores, and superior to that of most of the Mille- 

 pores : the pores or cells are very numerous, placed in 

 short curved lines, or dispersed on both surfaces ; all 

 those that are found on the same side, appear to com- 

 municate with each other by very thin perforated divi- 

 sions. The polypi of the two surfaces appear insulated 

 by means of a diaphragm, which is very thick, and 

 parallel to the plane of the two surfaces, dividing the 

 Polypidom in two laminaB of equal thickness. 



The colour of the Adeonas is an iron-grey, some- 

 times of a deep hue. 



They rise to two or three decimetres in height. 



GREY. 



1. Adeona grisea. Stem short; expansion al- 

 most orbicular or fan-formed, and pierced with os- 

 cules ; colour a deep iron-grey ; height about one 

 decimetre. — Plate 19. fig. 2. 



Australasia. 



ELONGATED. 



2. Adeona elongata. Stem long and tortuous, 

 sometimes branching; expansion long, and nearly 

 oval ; oscules inclining to oval ; colour whitish , 

 height two decimetres. 



Australasia. 



FOLIACEOUS. 



3. Adeona foliacea. Stem long and branching, 

 cylindrical, with foliated expansions, which are almost 

 linear, dispersed, or placed in clusters ; height from 

 two to three decimetres. 



Australasia. 



