238 
CLASS HI.— 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 laminae 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 branchings 
cylindrical, with foliated expansions, which are almost 
linear, dispersed, or placed in clusters ; height from 
two to three decimetres. 
Australasia. 
