GRAPTOLITES. » a 
Fig. 29. 
ppt pa tt tbl TALE od 
oer 
GRaApPToLitHus WHITFIELDI: 
twice enlarged. 
mucronate pomt extending from each angle of the cellule ; as also in 
G. testis of Barrande ; except that in the eBecuae species these appen- 
dages are more rigid. 
In Phyllograptus typus and P. ilicifolius, these processes are apparently 
the extension of the angles of the cell-partition. 
The cellules of Dendrograptus, Callograptus, and Dictyonema some- 
times show mucronate extensions from their outer margins. In Retiolites 
the cellules sometimes terminate in a plain margin, and in one species the 
divisions are extended in short strong mucronate points. (Plate B, 
figs. 5 and 21, and plate xvii, fig. 6.) 
All the species of Retiograptus have the margins of the stipes gar- 
nished with slender mucronate points, corresponding to the cellules, and 
extending almost rectangularly to the axis. (Plate xiv, figs. 6-9.) 
These ornaments are not always uniformly developed in the same 
species, or even in the same individual. In the larger proportion of 
specimens of G. ramosus, the margins of the cellules are apparently 
plain; but in the cellules of the simple part of the stipe we sometimes 
find a rigid mucronate point, prolonged from the upper margin or limit of 
the cell-aperture. (Plate A, fig. 20.) In G. seztans, the mucronate 
point is half-way between the two cell-apertures. 
In specimens of G. sextans, and in some allied forms from the Hudson 
