BULLETIN OF THE LABORATORIES 
156' 
spicuously narrower than the lateral rows, in sections made just above 
the epithecal membranes. The central cells often show a tendency 
towards a secondary horizontal arrangement, the lateral cells however 
have also a well-defined secondary diagonal arrangement, diverg- 
ing from the central rows of cells at an angle of about 15° above 
a line drawn horizontally across the surface of the frond. The small- 
er size of the mesial cells, and the diverging cells on either side give 
the frond a leaf-like or rather a plumose arrangement which is very 
characteristic. 
Cells angular below, quadrangular or rhomboidal ; rounded at 
their apertures, oval or almost circular ; arranged between longitudi- 
nal raised lines. Fragments of variable size have been found, often 
70 mm. long, without any evidence either of base or apex. Full grown 
specimens were probably 15 to 20 mm. in length. The broadest speci- 
men with perfectly parallel sides seen was 16 mm. broad ; the broad- 
est specimen of those of more irregular form measured 25 mm. from 
the mesial series of cells to the lateral edge, the entire width therefore 
was probably 50 mm. Mesial cells usually number 14 to 16 in a 
length of 4 mm; lateral cells, 10 to 14 in the same length. From 17 
to 19 lateral cells occur in a width of 4 mm. The mesial cells are 
narrower than the lateral cells, but the degree of narrowness is vari- 
able. 
There is not the least doubt of the identity of the first figure pub- 
lished with Phcenopora platyphylla, James ^ a form related to Ph. constel- 
lafa, Hall^ with which species, indeed, the authors compared our Ohio 
specimens. But the identification made by Hall, among the figures 
prepared by Van Cleve, evidently shows that the authors had an elon- 
gated species in mind which they considered typical. 
Again most of the distinct features mentioned in the original de- 
scription are those of Ptilodictya expansa. These are : “ fronds form- 
ing . . . elongate stipes, . . .. the lateral edges are 
generally parallel, . . . thin longitudinal partitions . 
slightly raised above the upper and lower walls of the cells, 
cells ... in horizontal, or nearly horizontal, rows, diverging 
from the central partition at an angle of about fifteen degrees above a 
horizontal.” The reference to maculae ” is of course a description 
of features belonging to the specimen of Phcenopora plaiypJiylla figured. 
There is some doubt as to the meaning of the words ‘‘central parti- 
tion” which I have italicised. If these refer to the narrow mesial cell 
