126 CANADIAN: FOSSILS. 
Genus. DENDROGRAPTUS,, Hall. 
Gr. Sevdpov, arbor, and ypadpw, scribo. 
Cole) to) 
footstalk, which is sometimes furnished below with a distinct root: or. root- 
like bulb, and above is variously ramified, and subdivided into numerous 
branches and branchlets, which are but slightly divergent ; the whole pro- 
ducing a broad spreading shrub-like frond : (fronds sometimes flabellate ?). 
Branches celluliferous on one side: cellules appearing sometimes as simple 
indentations on the surface, and sometimes distinctly angular, with the 
denticles conspicuous, In some specimens the cellules are indicated by 
prominent pustule-like elevations, arranged along the centre, or in sub- 
alternate order on one face of the branch. Substance of the stipe and 
branches corneous, solid or tubular: surface striated. 
These bodies present specific distinctions in the strength of the stipe or 
stem, in the mode of bifurcation and number of branches, in the character 
of the surface, and in the general form of the frond. ‘The celluliferous 
side usually adheres to the stone, and we perceive only some simple undu- 
lations or unequal thickening of the back of the branches. Often the 
branches have an alation on one side, like a thin pellicle flattened and 
extended along the more solid axis. ‘The radix or radicle consists of an 
expansion of the footstalk, and in one species appears like a flattened bulb 
or disc, of irregular form. ‘The footstalks, when well preserved, are 
marked by interrupted longitudinal striz, and the non-celluliferous faces of 
the branches are variously striated, the striz in most instances being 
unequal or interrupted in their course. 
In the study of the fossils of this general character, I have indicated 
the species from the Potsdam sandstone of the Mississippi valley as the 
typical form of the genus. In this one, the cell-denticles are quite con- 
spicuous and distinctly angular ; while in some of the species from the 
Quebec group, the form of the cell-denticles is obscure, and in others it is 
shown. only as a round or elliptical pit or pustule, depending on the con- 
dition of preservation. hese differences. in the form of the cellule lead 
me to suppose that a farther subdivision of this group may become neces- 
sary ;, but im the condition of the specimens in the collection before me, I 
do not feel justified in attempting to do this at the present time. 
There is likewise a gradation in the mode of growth among the species, 
by which there is an apparent transition from the form of Dendrograptus 
proper, to those similar to Dictyonema. I have thought it necessary to 
separate two forms of the latter type under another designation. 
The following figures, already published in the Geological Report of 
Wisconsin, illustrate the character of the species of ‘this genus from the 
Potsdam sandstone. 
Generie characters.—-Fronds simple or aggregate, consisting of a strong 
