OF DENISON UNIVERSITY. 
153 
which usually alternate between the keels of adjacent branches, but 
are opposed when situated on opposite sides of the same keel. The 
mesh-work thus formed is very beautiful. The openings correspond in 
number and situation to the cells beneath. Microscopical sections 
show the cells to be angular below, becoming rounded and circular 
above, and opening laterally upon the sides of the branches. About, 
three cells occupy the length of a fenestrule. 
The non-poriferous side forms the upper or inner face of the frond, 
and is the face usually presented. The branches are of medium size, 
from 5 to 6, usually 5.5 in the width of 2 mm, remotely bifurcated, 
connected by dissepiments. Dissepiments strong, two-thirds as wide 
as the branches, in some cases wider, in others narrower, about 4 to 
4.5 in the length of 2 mm. The branches appear smooth in perfect 
specimens, slightly striated longitudinally in worn specimens. The 
fenestrules are oblong in form, the corners rounded. 
Named in honor of Mr. E. O. Ulrich, to whose kind assistance I 
am in many ways indebted. 
The keels of Hemitrypa dubia^ Hall, are connected by continuous 
transverse bars ; this species is therefore a member of the genus Uni- 
trypa, Hall, and our Clinton species is undoubtedly the oldest species 
of Hemitrypa known. 
Locality and position. Brown’s Quarry, Clinton Group, common. 
PTILODICTYONID^, Zittel. 
Zoaria consisting of compressed branching or simple leaf-like ex- 
pansions, composed of two layers of cells, grown together, back to 
back, by the adhering of their epithecal laminae. Interstitial cells, 
when present, never in the form of vesicular tissue. 
Genus CLATHROPORA, Hall. 
Zoaria consisting of dichotomously dividing branches which anas- 
tomose at fairly regular intervals, forming a flabellate fenestrated frond. 
Interstitial cells entirely wanting. 
