GRAPTOLITES. 101 
with or without the dise, may be known by the short funicle, and the numerous 
subdivisions near the centre. The stipes differ from those of any other species 
in their proportions, and the form of the cellules and denticles. In these 
separated parts there is some resemblance to G. arcuatus; but that 
species has the stipes more curved, with a different form of cell-denticle, and 
is moreover marked by the frequent occurrence of the minute radicle 
attached to the separated stipes, as well as by the presence of cellules 
nearer to the origin of the latter. 
The great variation in the number of stipes shown to occur in G. 
Logant, as well as what occurs in a lesser degree in G. octobrachiatus, is 
sufficient evidence that strict specific characters cannot be founded on this 
feature alone, im species where the stipes are numerous. From what we 
are able to observe, it would appear that the disc of G. octobrachiatus 
extends itself with the age of the individual ; though in G. Logani there 
is no perceptible difference in the width of the stipes near the base, whether 
the discs are larger or smaller. In those specimens of this species which 
are without the central disc, or where this part may have been removed, 
the stipes are always more slender towards the base than when they are 
embraced within the central disc. 
The margins of the disc are slender, and sometimes found broken between 
some of the stipes, without injury to the rest of the body. The parts so 
broken assume the same outline as if entire, and may probably have been 
afterwards extended to correspond with the other portions. This feature is 
seen in plate IX, fig. 4, where a specimen preserving half of the disc 
shows that in three spaces between the stipes the disc had been partially 
broken away, and appears to have been in process of reproduction. 
In specimens showing the inner side of the frond, we find a distinct groove 
marking the centre, the funicle, and the bases of the stipes: this is seen 
whether the disc is preserved or not, and appears to be an organic feature. 
This groove, corresponding to the central axis, likewise extends for some 
distance along the celluliferous portion of the stipe; and the indentation, 
being thus interrupted along the centre, is shown more strongly on each 
margin, appearing like a double indentation or serrature. 
On the opposite side of the frond, when well preserved, the stipes near 
their bases, often appear to have a double axis, or an elevation on each 
side. This feature seems to be due to pressure, or to the filling of the 
tube on the two sides, while the centre has been contracted. It is clearly 
an accidental feature, probably dependent on the nature of the surrounding 
material, at least in part, smce some specimens from their origin are full 
and round on the back of the stipes. 
G 
