120 CANADIAN FOSSILS. 
apertures mucronate by the continuation of the cell-partitions, the mucro- 
nate appendages sometimes appearing to be double, as if each angle of 
the aperture had been thus ornamented.* Central axis linear, from half a 
line to nearly a line in width. In some examples there is an apparently 
greater width, which is probably due to a slipping of the test. This 
central axis is often crenulate from the bases or impressions of cellules of 
the other division, which is rectangular to that part of the frond pre- 
served. 
This species assumes a variety of forms, and, from an examination of 
specimens of the extremes, they might be regarded as distinct species. 
After examining several hundred specimens however, I am not able to 
find constant characters to establish specific differences. The individuals 
figured represent the principal varieties. I have not thus far observed 
forms intermediate between the short broad and the elongate-oval ones, 
but they may be found im larger collections. The number of cellules in 
entire fronds varies in different individuals from twenty-five to fifty on 
each side, according to the size and form of the specimen. 
The specimens are all compressed, and the rectangular arrangement of 
the parts of the frond, as seen in P. dlicifolius, cannot be seen in these; 
the evidence of this character being the serratures along the central axis, 
which are transverse to those of the two sides. The proportions of length 
and breadth vary extremely ; one of the broad forms has a width of five 
tenths of an inch, with a length of eight tenths of an inch, while a long form 
is two and an eighth inches in length and six tenths of an inch wide m 
the widest part. 
In a single fragment of the shale containing this species, the number of 
individual stipes within a small space is so great as to suggest the proba- 
bility that these have originated from a common axis, as in Ltetiograptus, 
and have been separated but a little distance from their centre of attach- 
ment. With one exception, all these are of small size, and present no greater 
variation than is observed in the stipes of a single frond of etograptus, 
fig. 9, plate xiv. 
EXPLANATIONS OF FIGURES OF PHYLLOGRAPTUS TyPUS, Hall. 
Puate XV. 
1. An extremely short and broad form of this species, with the axis broad, and 
showing some remains of the cellules at the base of the separated division. 
2. An elongate-ovate form of stipe, with a broad axis, which does not show 
remains of cellules. Some of the cellules in the upper part of the stipe are 
filled with iron pyrites. 
> _________ 
* This feature may possibly be sometimes due to the overlapping of two adjacent 
folia, so as to bring the cell-partitions and cell-denticles near to and parallel with 
each other, showing a denticle from each one. 
