132 
encrusting stones and forming its cells like a Fluslra, in largo 
circumscribed patches. The first appearance of its rising 
into a lamellated form, is the production of detached ridg eS 
and papillary eminences, as these become more elevated they 
assume the form described above. 
The growth of the cells appear to be periodic and rapi ! * ’ 
formed, in the first place very delicately, and afterwards 
completed and strengthened by depositions of calcareous 
matter. In almost every specimen, bands of this periodic 
growth are to be seen varying from half-an-inch to one inch 
in depth. If these bands be carefully examined it will b 0 
fount!, that all the cells composing them are nearly in th e 
same condition of growth; each band differing from l " e 
other. lienee the polypidom is frequently marked by ridg eS ’ 
which indicate the extent of the various enlargements; a ot 
the whole process of the growth of the cells, from the mere 
gelatinous effusion, to the complete obliteration, can be °h' 
served in a single specimen. 
The form of the cells varies with the form of the pol)" 
pidom, yet every change can be considered but as variation 
of one form from mechanical causes. When the extension 
takes place in the encrusting form, the effusion of the pulp 1 
more extensive than in the erect and foiiaceous state. 
this, lime is rapidly deposited and the cells appear larger an ‘ 
not so much crowded as in the other kind, so that the grow 
is effected here as it is in Lepralia, Flustra, &c. The cel s > 
which are superficial and on both sides of the leaf whe 
erect, stand on a solid base which unites both surface* 
They present three varieties of appearance the first of whm 
is the semi-gelatinous or pulpy slate, the second where 1 
surface is granular, from the fully developed cells, and l . j 
third is the confused appearance produced by the parh u 
and complete obliteration of the cells. 
ALCYONIDCLiE. 
|Jg 
Polypidoms sponge-like, fleshy, polymorphous; the c ® 9 
irregular in disposition, immersed, and concealed with 
contractile non-opcrculate aperture. 
ALCYONIDIUM. 
Generic Character-. “Polypidom fleshy, lobed, or crus^ 
ceous ; cells immersed, pentagonal, with iibro-corne 
parietes, the aperture terminal, simple, contractile. ■’ 
pes ascidian.” 
SEA RAGGED STAFF. ( A. Gelatinosum. ) ^,jy 
pidom fleshy, cylindrical, slightly compressed, irregm 
branched or lobed, smooth. 
a9i 
Fucus Spongiosus nodosus, Raii Synop., vol 1, P*.^' 
no. 42. Aleyonium, seu fucus nodosus et spongiosus, & 
