28 CANADIAN FOSSILS. 
In specimens stripped of the test, where the interior has been filled with 
stony matter, the cell-partitions present the appearance shown in fig. 3, 
plate A; while there is a large central space apparently occupied by the 
common body, but without the appearance of a central axis on the exterior 
surface. When the surface is ground down to a plane intermediate between 
the exterior and the centre, it presents the aspect of fig. 4 ; and when the 
cutting is carried to the centre, it gives the characters of fig. 5, the cell- 
divisions apparently reaching to the axis. 
The general form of this stipe in section (fig. 6) approaches that of 
Retiolites, as shown by Barrande and Geinitz; and in the arrangement of 
the common body and axis there is a departure from the typical diprioni- 
dian forms of Graptolithus. In this transverse section we have a some- 
what concavo-convex form, which is narrower on the concave side. There 
is a central or sub-central point indicating the filiform solid axis; and on 
each side of this are the divisional cell-walls, which produce a shght con- 
traction of the exterior walls of the stipe at the inner limit of their attach- 
ment. Another section, fig. 7, shows the same features, together with the 
remains of two other cell-divisions, neither of which reach to the exterior 
walls of the graptolite; and the one on the right hand shows the narrow 
extremity just before joining the axis. 
These sections, together with numerous other longitudinal, transverse 
and oblique sections, compel us to conclude that this graptolite possesses 
a filiform central or sub-central apparently solid axis ; and that the cell- 
partitions originate from, or are joined to this axis. ‘These cell-partitions 
appear to consist of triangular plates, which have an unequally arching or 
convex upper surface, and a concave lower surface. ‘This form of cell- 
partitions would Jeave the alveoles to communicate at their bases with the 
common body on each side.* 
In some forms having cellules of this character, as in G. bicornis proper, 
there is, in the flattened stipes, an external ridge, as if indicating the june- 
tion of the axis with the external walls. But in examples where this axis 
extends beyond the celluliferous portion of the stipe, it is compressed, 
having the aspect of a flattened cylindrical filiform body. It has no 
appearance of haying been flat, or laterally extended within the body of 
the stipe. 
In the ordinary forms of graptolites the orifice of communication between 
the cellules and the common body is eal round, oval, or quadrangular ; 
* The cell-partitions in this form of graptolites are represented as they appear to exist 
in the solid specimens examined, on plate A, fig. 9; where, curving gently downwards 
on their exterior margins from the upper edge of the orifice, they turn more abruptly 
towards the axis, while the central portion extends obliquely to the axis, leaving a 
broad arch above, which gradually becomes angular as it approaches the axis. 
