30 CANADIAN FOSSILS. 
In the bi-celluliferous species the compressed specimens present the 
plane of the orifice, sometimes rectangular to the general axis, sometimes 
with the outer margin a little advanced, makmg an acute angle with the 
axis of the cellule, while sometimes the plane of the margin of the aperture 
is rectangular to the axis of the cellule, or rarely makes with it an obtuse 
angle. ‘The cellules of Retiograptus, which have not yet afforded means 
of satisfactory examination, apparently have their orifices nearly rectan- 
gular to the general axis of the stipe. 
In one of the forms of the bi-celluliferous graptohtes the cellules are 
sub-elliptical tubes, with an orifice of corresponding form, without extension 
beyond a slight thickening or callosity at the margin of the orifice. The 
plane of the cell-aperture in this one makes an obtuse angle with the 
direction of the general axis. 
In forms like . dicornis the external orifice is transversely oval, with 
or without a projection and thickening of the test from the cell-partition 
above the orifice, or extension of the test. 
4. Ornaments of the Test.—The compressed condition in which the 
graptolites usually occur is unfavorable to the preservation of any minute 
surface-markings, or ornaments of the test. 
In many of the species, fine striz, parallel to the margins of the cell- 
apertures, are perceptible, and in the larger number of species this mark- 
ing is all that is preserved. There is sometimes a granular appearance 
of the surface, but I have not been able to satisfy myself that this is the 
actual surface-texture ; it may be a condition induced by mineralization. 
In a few examples there is a row of minute pustules at the base of, and 
corresponding to the cellules. 
The stems and branches of Dendrograptus, Callograptus, and Dietyo- 
nema are irregularly striated. In typical species of Retzolites the test 
is finely reticulate ; while in the species from the Quebec group, this 
texture, if existing, is so fine as not to be readily resolved by an ordinary 
lens. The surface however has not the appearance of entire smoothness, 
as in most of the ordinary graptolites. 
The chief ornaments of these bodies are the mucronate extensions of 
the test, usually from the lower margins of the cellules, but sometimes 
from the upper margins. In ordinary forms of the species, with single, 
and with double ranges of cellules, the mucronate or setiform extensions 
are usually from the lower extremity of the cell-aperture, as illustrated in 
fig. 29. 
In all those forms of which G. bicornis may be regarded as the type, 
these processes, when existing, are extensions of the test above the aper- 
ture, so far as observed (pl. A, figs. 1, 8, 9); or as in species of the 
character of fig. 20, plate A. 
In some species, as G. quadrimucronatus (plate xii), there is a 
