GRAPTOLITES. - Al 
of the stipe at its base. In other specimens we have a crescent-shaped 
extension, as if the disc were in process of development, or perhaps of 
absorption. Much the larger proportion of the specimens of this species, 
however, are destitute of disc or bulb, and have every appearance of 
being complete without this appendage. 
These aspects of the species are shown on plate A, figs. 18, 15, 16, 
and 17. 
How far the bulb-like appearance at the base of some of the species of 
Dendrograptus may correspond to the disc of G. bicornis, I have not at 
this time the means of satisfactory determination. 
§ III.—tTHE NATURE AND PARTS OF THE STIPE PROPER. 
1. The solid axis. 
2. The common canal, 
3. The calycles or cellules. 
4, Nature and ornaments of the test. 
1. The Solid Avis.—All the graptolites proper have been found to be 
provided with a slender solid axis,* while this feature has not been satis- 
factorily proved in regard to Dictyonema, and to some other forms. 
In those species having a single series of cellules, this axis is upon the 
back of the stipe, or on the side opposite to the celluliferous margin; and 
in the branching forms it follows all the ramifications. In all the speci- 
mens where it has been observed, it is a slender cylindrical or flattened 
filiform solid body. In some extremely compressed specimens, this axis 
appears as a slender elevated ridge along the back of the stipe; and 
where the substance of the body has been removed, it leaves a narrow 
groove along the margin of the impression. 
In the examination of large numbers of specimens of the monoprionidian 
species, we have never found the axis prolonged beyond, or denuded of, 
the cellules; as shown in G. colonus, by Barrande, in his Graptolites of 
Bohemia. (Plate ii, fig. 5, of that memoir.) 
In all the specimens where the extremities of the stipes are entire, as 
represented in plates i, ii, and iii of this memoir, there is never any 
extension of the axis beyond the last partially developed cellule; and 
the number of specimens in this condition is considerable. 
Tn the graptolites with two series of cellules, the solid axis is very 
* In those species with a single series of cellules, M. Barrande has ascertained that 
this axis is solid and cylindrical, its diameter not exceeding 4 millimetre, and its struc- 
ture apparently fibrous. (Graptolites de Bohéme, page 4.) 
B 
