OF DENISON UNIVERSITY. 1 63 
a fragment) seen. The specimen is 26 mm. long and 22 mm. broad, 
being divided dichotomously into branches at angles of about 45°. 
The branches are 3 mm. wide and scarcely ^ mm. thick. The 
cells are arranged in longitudinal series, forming at the same time more 
or less accurate oblique cross-rows. Cells oval, narrow in the middle 
rows, broader in the lateral rows, about 6 occupying a length of 2 
mm, and ii series the same distance in breadth; 10 to 13 series are 
found on the various branches. The longitudinal series are separated by 
raised longitudinal lines, inclined to be flexuose on account of the diagonal 
lines, in which the cells dispose themselves ; occasionally these ridges 
seem to bear 2 or 3 fine striae. The margins of the branches show 
faint traces of striae. 
From the succeeding species it may be distinguished by the thin- 
ness of its branches, the wider non-poriferous margin, and the greater 
number of its cells in transverse measurement. Name signifies thinned 
or grown thin. 
Locality and position. Soldiers’ Home Quarry, Clinton Group. 
XI. Pachydictya bifurcata, {Van Cleve) Hall. 
{Plate XV, Fig. 9; Plate XVII, Fig. 9.) 
Stictopora bifurcata, (Van Cleve) Hall, 1883, 12th Indiana, Geol. Report. 
Frond arising from a narrow stipe, attaining the size of the branch- 
es above, then branching rapidly below, less frequently above, at an- 
gles between 30° and 50°. The branches are convex and decidedly 
thickened, their thickness exceeding half their width. The surface 
even and smooth, at least not tuberculate, channeled lengthwise, the 
cells placed in the channels, five and a half or six found in a length of 
2 mm, and six or seven in the same distance in breadth. The cells 
are oval, slightly separated at the ends by the dividing lamellae ; the 
longitudinal series are usually separated to quite a marked degree by 
thick lamellae, which are marked longitudinally along the summit by 
faint undulating stri^. The edges of the branches are non-poriferous 
and smooth, or very indistinctly striate, obtuse, but with a narrow sa- 
lient margin indicating the position of the epithecal lamina. 
The largest specimen found was 160 mm. long and 85 mm. wide; 
the branches are somewhat flexuose, about 4 to 5 mm. broad, and 
