OF DENISON UNIVERSITY. 
165 
The surface is tuberculate ; the tubercles are of variable distinctness, 
and are arranged in something like order, from 4 to 5 in a distance of 10 
mm. The tissue in the tubercles becomes very thick, the arrange- 
ment of the cells is somewhat disturbed and their number reduced. 
The largest fragment at hand is 55 mm. long and 35 mm. broad. 
The branches vary from 6 to 9 mm. in width, and from 1.8 mm. to 
3.5 mm. in thickness. 
Name signifies thicks swollen, referring to the thickened fronds. 
This form may be compared with P.fenestelliformis, Hall, as identified 
by Mr. E. O. Ulrich, from the (hncinnati Group of Illinois. 
Locality and position. Soldiers’ Home Quarries, Fair Haven, Clin- 
ton Group. 
XIV. Pachydictya obesa, sp n.. 
{Plate XV, Fig. 12.) 
The structure of this species is very similar to the last, but the 
fronds are broader, apparently undivided, and usually thicker, forming 
coarse, often undulating or folded fronds. Tubercles much more dis-^ 
tinct, with a more decided tendency for arranging themselves in series, 
4 to 5 in a distance of 10 mm. 'Tangential sections show that the 
number of cells is decreased in the tubercles by the turgescence of the 
surrounding laminae, or by the entire suppression of cells. One of 
the largest fronds at hand is a Iragment 65 mm. long, 37 mm. wide 
and 5 mm. thick. Some specimens are not so thick, but still thick 
enough to attract attention to this feature. It may be compared with 
P. gigantea, Ulrich, from the Cincinnati Group of Illinois. 
Name signifies, very thick "and swollen, fat. 
Locality and position. Soldiers’ Home Quarry, Clinton Group. 
CYSTODICTYONID.^, Ulrich. 
Zoaria consisting of two or more layers, grown together along their 
epithecal membranes. Cell apertures with a crescentic lip. Intersti- 
tial spaces occupied by vesicular tissue, which in the matured stage is 
almost obliterated by a secondary deposit of sclerenchyma, apparently 
