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BULLETIN OF THE LABORATORIES 
from 2 to 3 mm. thick. This form may be compared with P. acuta ^ 
Hall, from the Trenton Group of New York. 
Locality and position. Soldiers’ Home Quarries, Fair Haven. 
Clinton Group. 
XH. Pachydictya bifurcata, var. instabilis, var. n. 
[Plate XV, Fig. 10.) 
Frond known only by fragments 30 to 40 mm. long and broad, 
branching dichotomously at wide and variable angles. The branches 
from 3 to 5 mm. wide and from i to almost 2 mm, thick ; the sur- 
face uneven, more or less tuberculated, the tubercles low but gener- 
ally distinct, without evident arrangement, about 4 tubercles in a dis- 
tance of 80 mm, measured longitudinally. 
The cells are oval, from 6 to 7 occupying a length of 2 mm, usu- 
ally nearer the latter number, and from 8 to 9.6 rows occupying the 
same distance in breadth. The non-poriferous edges narrow in the 
specimens examined. 
Whether this form is distinct from the last one, it is difficult to 
tell. Where there are so many species of a genus, occurring in such 
abundance, their form is usually very variable, and the distinctions 
between species are not always well defined. Judging from the speci- 
men at hand, it is difficult and perhaps impossible to distinguish be- 
tween the forms specifically, and intermediate forms seem to occur. 
Locality and position. Brown’s Quarry, Clinton Group. The 
species occurs here in all its forms apparently. The extreme, nodu- 
lated or tuberculated forms, which are separated here as a variety pre- 
dominate. 
XHI. Pachydictya turgida, sp n.. 
[Plate XV, Fig. 11; Plate XVH, Fig. ii.) 
Fronds variable, branching dichotomously at angles from 30° to 
50°; branches more or less thickened, the edges inclined to be obtuse 
with a salient line along the epithecal lamina, the margin non-porifer- 
ous. Cells oval, 12 in a distance of 5 mm, measured along the lon- 
gitudinal series, 16 series in the same distance in breadth. Two or 
three faint flexuose lines are found on the ridges separating the series. 
