101 
The Polypiaria which have stony corals are RQOM Xi 
separated 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 with a horny operculum, and 
the cells themselves are placed side by side, so 
as to form a variously shaped stony coral. 
In some of these the pores are placed on all 
sides of the coral, which has often an arborescent 
form, as in the genera Millepora and Seriato - 
pora , which are cylindrical and branchy, and 
Adeona and JEschara , which are fiat and folia- 
ceous. The first of these is 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, as the Retepores , the cells are short 
and not prominent, and the coral foliaceous, 
and variously netted together. In others, as 
the family of Tubulipores ( Tubuliporidce ), the 
cells are long, subcylindrical, and more or less 
prominent on the surface. These corals vary 
greatly in shape; in the Frondipora they are reti- 
culately branched, and the cells placed in irre¬ 
gular tufts, whilst in the Hornera , which has 
nearly the same form, they are placed in regular 
order; in the Tubulipores and Obelia the cells 
are tubular, and crowded together on a cup¬ 
shaped crust; the genus Idmotea has the same 
shaped 
