76 
BULLETIN OF THE LABORATORIES 
with wavy margins. The size of the serrations extremely variable ; 
some of the most prominent seen being 1.4 mm. wide, 4 serrations 
taking up a length of 9 mm. Cell apertures distinctly lipped on one 
side, the lips not directed in definite related directions as far as known; 
the apertures are not arranged in well defined lines, however, some 
arrangement can always be discovered. Usually this consists in a dis- 
position of the cell apertures in oblique intersecting lines across the 
sides of the branches ; one of these oblique series can usually be readi- 
ly seen, the other set are sometimes imperfectly developed; when 
these oblique series are both well developed, longitudinal series are 
necessarily present, although even in that case these longitudinal lines 
run somewhat diagonally along the stem. In other words, diagonal 
rather than longitudinal arrangement prevails. In the serrations the 
cells are always more compactly arranged. Along the indented por- 
tions, however, there is always a crescentic space, variable in size, 
along which there are no cells, the margin is therefore interruptedly 
celluliferous. As may be imagined from some of the remarks above, 
the number of cells is variable. In one specimen 5 cells occurred in 
a length of 2 mm. Interiorly the cells are surrounded by vesicular 
tissue, irregularly arranged. 
Meek clearly did not understand his own specimens; he did not 
know that the branches were three-sided, but gave a thickness of .04 
inch to his branches, supposing them to be flat. He also failed to no- 
tice the distinctly projecting apertures of the cells with irregular lips. 
White described his species from the Coal-measures at Danville, Illi- 
nois, and states in a later publication that the type specimens were ob- 
tained from Mr. William Gurley. I therefore applied to Mr. Gurley 
for specimens he considered authentic, and received all he had. White 
could not recognize the three-sided branches in Meek’s description and 
so proceeded to describe his specimens as Pt. triangiilata^ and also 
states that the cells are irregularly disposed at the surface. Specimens 
at hand, from the original source, however, show the same arrange- 
ment of the cells as noted in the Ohio specimens. Indeed, some of 
the specimens from Danville show the oblique intersecting series very 
beautifully. It must be remembered, however, that although diagonal 
intersecting series are considered typical, most specimens are to some 
extent variations from this type, however, even then they rather pre- 
sent cases of disturbed regularity than typically irregular disposition. 
The width is stated as varying from 3 to 5 mm; this is broad enough 
