GRAPTOLITES. 139 
their origin or union with the branch, and slender in the middle; from 
about one third to one half as wide as the branches. Cellules undeter- 
mined. Surface smooth. 
This species is associated with D. robusta. It is a less robust form, 
the branches are not more than one half as wide, and the fenestrules not 
more than one third the length of those in that species, while the connecting 
filaments are quite as strong. ‘The specimens are extremely compressed, 
and the character of the cellules cannot be determined. 
While the preceding species all have the characteristics of true 
Dictyonema, in none of them has the base been discovered, and the entire 
form of the frond is therefore unknown. From the strong growth of all of 
them, and the nearly parallel direction of the branches, we must presume 
them to be fragments of very large fronds. 
ExpLANATION oF Figures or DictyonemA Morrayi, Hall. 
PuatE XX. 
6, 7. Fragments of two fronds ; the figures of the natural size. 
Formation and Locality.— Quebec group; Point Lévis. 
Genus PTILOGRAPTUS, Hall. a. g.) 
Gr. rriAov, pluma, and ypadw, scribo. 
Generic characters.—Frond plant-like, rooted ? simple or branching. 
Branches and branchlets plumose, the pinnules rising alternately on opposite 
sides of the branches ; celluliferous on one face only: branches cylindrical. , 
or flattened. Substance corneous, dense ; apparently smooth exteriorly, or 
corrugated by compression, or during fossilization. 
In general habit this genus resembles the modern Plumularia, and 
its mode of growth was probably similar. We know at the present time 
two species, one a slender and delicate form, the other more strong 
and coarse, and differing in its irregular mode of branching; while 
at the same time the smaller branches and pmnule resemble the other 
species. The cellules are distinctly confined to one face of the pinnulee ; but 
whether arranged in a single linear series, or in alternating order, cannot 
be satisfactorily determined. Both species are in soft shales, associated 
with Graptohthus Logant, G. quadribrachiatus, G. arcuatus, G. Bigsbyi, 
and others. 
