202 The American Geologist. April, 196% 
In order to make the points of similarity and dissimilarity 
still more emphatic the characters given in the above descrip- 
tions may conveniently be arranged in three parallel columns: 
HETEROTRYPA 
Zoarium growing 
from an expanded 
attached base’ up- 
ward into a_ simple 
often undulated or 
irregularly inosculat- 
ed frond or _ occa- 
sionally into flat 
branches, 
Cells polygonal to) 
circular. 
Cell walls thin to 
thick. 
Mesopores few to 
numerous, always 
angular, 
Acanthopores — small, 
usually numerous. 
Present only in the 
peripheral region. 
Diaphragms 
straight and of one 
kind, more numerous 
in the mesoperes and 
always more crowded 
in the mature than 
in the immature re- 
gion, 
Walls —_ apparently 
amalgamated with 
one another. 
DEKAYELLA 
Zoarium growing 
upward from an at- 
tached base into cyl- 
indrical often com- 
pressed branches. 
Cells rounded or 
ring-like. 
Cell walls some- 
what thickened  to- 
ward the surface. 
_ Mesopores numer- 
ous. 
Acanthopores of 
two sizes, large and 
~ small. 
Large ones present 
in the arial region, 
Diaphragms 
Straight and of one 
kind more numerous 
in the mesopores and 
always more crowd- 
ed in the mature 
than in the immature 
region, 
DEKAYIA. 
upward from an ex- 
panded basal attach- 
ment into rarely cyt- 
indrical usually flat- 
tened branches, Oc- 
casionally subfrond- 
escent. 
Cells folygona/. 
Cell walls thin. 
(Thick in one spe- 
cies. ) 
Mesopores few to 
none, 
Acanthopores us- 
ually few and of 
large size. Some- 
times fairly numer- 
ous. Present in the 
axial region. : 
Diaphragms from 
almost none to mod- 
e rately abund- 
ant. More abundant 
in the mature region. 
A thin pellicle 
sometimes drawn 
over the mouths of 
the zocecia. 
The characters with which we have to deal are therefore: 
1) The type of growth, whether (a) ramose or (b) fron- 
descent; 2) the thickness of the walls; 3) the character of the 
acanthopores whether (a) large or (b) small or (c) both 
large and small; 4) the presence or absence of a pellicle clos- 
