73 ' 
This class may be arranged in groups, characterized 
by the substance of the coral. 
The Polypiaria which have stony corals are divided 
according to the structure of the cell which the Polypes 
inhabit. In the first of these, the mouths of the cells 
are terminated and often closed by a horny operculum, 
and the cells themselves placed side by side, so as to 
form a variously shaped stony coral. In some they are 
placed on all sides of the coral, which is often cylindrical 
and arborescent ( Millepora and Seriatopora) ; or flat, 
and foliaceous ( Adeona and Escharis). The Adeonae 
are peculiar for the base of the stems which support the 
leaves being jointed, like the stems of the Isis hippuris. 
Others have the cells placed only on one side, the 
coral being usually attached by the other. In some 
( Retepora ) the ceils are short and not prominent, and 
the coral foliaceous, and variously netted together. 
In others, as the family of Tubuliporae ( Tubuliporidce), 
the cells are long, subcylindrical, and more or less pro¬ 
minent on the surface. These corals vary greatly in 
shape; thus in some they are reticulately branched, and 
the cells placed in irregular tufts ( Frondiporo ), or in 
regular order ( Hornero ); or the cells are tubular, and 
crowded together on a cup-shaped crust ( Tubulipora 
and Obelia) ; and, lastly, one genus ( Idmotea ) has the 
same shaped cells, but they are placed in lines across 
the two upper sides of a triangular arborescent coral. 
The cells of the Celleporae (Cellopora) are distinct^ 
ventricose, vasiform, with a round mouth, and united 
together into a spongy coral: two genera ( Berenice 
and Discopora) consist of similar cells, sunk into an 
expanded chalky crust. 
In the second division the mouths of the cells are 
bilabiate, and the cells themselves are united laterally 
on one or two planes into a crustaceous, or arborescent 
coral. In some ( Flustra ) the cells are very flat, and 
placed in a regular manner, forming a crust on marine 
bodies, or on one or both sides of an expanded foliaceous 
coral. In others {Electro) the cell is ciliated, and placed 
round 
ROOM XI. 
Nat. Hist. 
