GRAPTOLITES. 45 
typical forms are so slight as to offer no sufficient ground for generic 
separation. 
There are however a few examples, where the stipe is marked by a 
range of cellules upon each side of the central axis, which appear to be 
properly separated from Diplograptus, on account of the form and structure 
of the cellules. These are apparently quite unlike those of G. pristis, and 
others of that sub-genus. The Graptolithus bicornis, and two or three 
allied forms, when flattened in the shale, show, as already described, a 
simple semi-elliptical notch in the margin of the stipe, nearly rectangular 
to the axis. This is well shown in fig. 3, plate vi, of M. Rarrande’s 
memoir, and also in Mr. Salter’s illustrations of Graptolithus teretiusculus 
of Hisinger.* It is represented, less perfectly, in the figures of Prof. 
Harkness,j and in most of my own figures on plate lxxii of the first 
volume of the Paleontology of New-York. When compressed rectangularly 
to the cellules, the apertures are transversely oblong-oval ; and the same 
form is shown when looking upon the celluliferous margin of an uncom- 
pressed stipe. 
The structure of these stipes and their cellules has already been 
described in a preceding section, with reference to the figures illustrating 
the same. The G. bicornis, renin im New-York and Canada, may be 
considered the type cf a group of species of which we have two in the 
shales of Norman’s Kill near Albany, one in Ohio, and a similar or identical 
form in the Utica slate at Collingwood in Canada West. I would include 
in the same group figs. 5 and 6 of plate iii, as well as figs. 7, 8, and 15, 
plate 11 of M. Barrande’s Memoir; Graptolithus teretiusculus of Hisinger ; 
and those referred to the same species by Salter.t The Diplograptus 
rectangularis of McCoy |] is of the same type, as also figs. 1, 5, 10, 
11, 12, etc., tab. ii, of Geinitz (Graptolithen) ; and I conceive that 
many, if not all of the scalariform specimens, belong to species of this 
character. 
The Graptolithus ramosus has usually been arranged by authors under 
Diplograptus ; the lower part of the stipe having a double range of 
cellules, while it is bifurcated above, with the cellules on the outer margin 
of each division, as already described; and a simple explanation of this 
condition has been offered by supposing that the solid axis has been 
separated after the death of the zoophyte. This however will scarcely 
afford a satisfactory argument when we find that all the specimens are in 
the same condition ; that usually the division begins at a uniform distance 
from the base ; and that, when entire, the divided portion much exceeds the 
* Quarterly Journal of the Geol. Society of London, vol. viii, pl. xxi, figs. 3 and 4. 
{ Id. Ibid., vol. vii, pl. i, fig. 11. 
ft Quarterly Journal of the Geological Society, vol. viii, pl. xxi. 
|| British Paleeozoic Fossils, page 8, pl. xiii, figs. 8, 9, and 10. 
