(di) 
ee) 
CANADIAN FOSSILS. 
§ V.—MODE OF EXISTENCE. 
he numerous individuals of entire or nearly entire fronds illustrated 
in this memoir, as well as Jarge numbers of others examined, serve to give 
a pretty clear idea of the general form of the true Graptolites, as well 
as of their congeners of the same family. Notwithstanding the presence 
of the radicle or initial point observable in so many species, it does not 
afford evidence of attachment to the sea-bottom or to some other sub- 
stance, at least in the mature condition. In all the monoprionidian forms, 
however much or little extended the radicle may be, it is always smooth, 
and tapering to a pomt. In many of these, and more especially in those 
with a central disc, this radicle is reduced to a minute protuberance, and 
is often scarcely or not at all perceptible. 
The same is essentially true of the greater number of diprionidian 
forms examined. In these the solid axis is sometimes extended beyond 
the base of the stipe, and terminated as if broken off abruptly ; while 
there is often a slender oblique process on each side of the base. 
In Retiograptus and Phylloyraptus there is not the same evidence of 
completeness at the base of the radicle. The lower termination, when it 
can be fully examined, is broken, as if there had been a further continua- 
tion of this part, though it exhibits no enlargement. I have inferred that 
all these, like the example of Retiograptus eucharis (fig. 9, pl. xiv), 
have constituted parts of a similar compound body, and are bué the separ 
rated stipes of the frond. If this be true, their mode of existence is not 
unlike the other species with compound fronds and a central disc. 
In G. bicornis the extension of the solid axis below the base of the stipe 
is not always preserved ; but when it is entire, we find two strong, diverging 
and slightly curving processes or spines from the base, having smooth 
terminations. Sometimes a dise or bulb, of the same substance as the stipe, 
extends between these spines, and in the compressed condition envelopes 
a few of the lower cellules, as shown in fig. 17, plate A. Some of the 
phases presented by the basal extremities of this species are shown in 
figs. 18, 15, 16, and 17 of the same plate. 
The expansion at the base of this species has the same general appear- 
ance as the central dise of G. Logani, G. Headi, and others ; showing that 
this sort of development of the substance is not alone characteristic of 
those forms having several stipes united at the base. In other examples 
this basal expansion is contracted in such a manner as to give a crescent- 
form to the lower extremity ; but in all these gradations, the margins of 
this part are entire and unbroken. 
We have seen that the youngest forms of the diprionidian graptolites, 
those which we may suppose had but recently escaped from the reproduc- 
