GRAPTOLITES. 49 
been able to determine clearly the existence of a solid axis. The cellules 
are indicated by angular processes or cell-denticles on the inner side of 
the branches ; as shown in fig. 5 of plate B. 
In the genus Rastrites of Barrande the distinguishing features are the 
slender cylindrical stipes or branches, with distant slender tubular cellules. 
The few species of Zhamnograptus known consist of cylindrical or sub- 
cylindrical stipes, with slender elongate alternating pinnulz or branchlets. 
No evidence of cellules has been observed in any a the specimens. 
The peculiar forms for which I have proposed the name Ptilograptus, 
consist of branching stems, which, in all their divisions, are studded on 
each side, in alternating order, with narrow pinnule. These are some- 
times extremely slender, or even capillary in their dimensions. In one 
species I have detected elliptical spots upon one face of the pinnule, 
which are slightly flattened, and I infer that these are the cell-apertures. 
The substance of the test is corneous, and there is an internal solid axis. 
Although I have placed these forms under the Graptolitide with some 
hesitation, the form of cellules may perhaps render a separation desirable ; 
but with only our present information, such a separation cannot at this 
time be made. 
The genus Jnocaulis was proposed for some flattened stipes with a scab- 
rous surface, which have the appearance of denticles upon the margins. 
These stipes grow in close groups or tufts, and are bifurcating or branched 
in their upper portions. No positive evidence of cellules has been observed. 
The presence of denticles, together with a corneous or carbonaceous sub- 
stance, have induced me to place this fossil among the Graptolitide. 
There is still another form known, which may be doubtfully classed 
among the Graptolitide. It consists of a slender flexible median rachis, 
on each side of which are placed, in alternating order, slender flattened 
pinnulz, which are of nearly equal width inomeboe and are themselves 
flexuous. Upon one side of the rachis are minute points or dots, which 
have apparently been the cell-apertures. The test is a black corneous 
or carbonaceous substance, but there is no evidence of a solid central axis. 
These bodies are numerous in some shaly beds of the age of the Trenton 
limestone, at Plattville, Wisconsin. For these I have proposed the name 
of Buthograptus.* 
Associated with the preceding forms, there are some stems of corneous 
or carbonaceous texture, frequently branched, the branches again dividing, 
and sometimes, if not always, in whorls; in one of which six divisions 
were counted. The general form of the body is not unlike that of Den- 
drograptus, but the branches are more slender, and ramify in a different 
manner, while there are no visible cellules. ‘Without farther knowledge, 
* Report of Progress of the Geological Survey of Wisconsin for 1860, p. 19; commu- 
nicated January Ist, 1861. 
