100 
room^xi. or j n t } ie ull( ] er surface being free and destitute 
of stars. 
The genera Sarcinula and Lithodendron are 
very like the star-stones, but the cells are 
cylindrical and prominent, and instead of being 
arranged side by side in one mass, they are, 
in these genera, united together by cross bands 
of calcareous matter, between which there is 
often placed a cellular structure, and in their 
young state the cells are prominent, and spring 
from a flat calcareous expansion. 
Some fossil genera have much the appearance 
of the Star-stones ( Astrea ?), Their cells are 
aggregate, side by side, forming a rounded mass, 
but they are quite separate from each other; 
these masses increase in size by new cells spring¬ 
ing from the centre or margin of the older cells, 
as in the genera Acervularia, and Strombodes. 
It may be remarked, that in the thin extremities 
of the Arborescent Corals, the cells often appear 
proliferous from the side of each other. 
The Cases 9 to 12 contain the Polypiaria. 
The Polypes of this class differ from the Sea- 
Anemones in the mouth being provided with only 
a single series of long tentacula, the body 
being more slender, and in the cells which they 
form being quite simple, or without any radiating 
laminae. 
This class may be divided into distinct groups, 
characterized by the substance of the coral. 
The 
