GRAPTOLITES. 105 
GRAPTOLITHUS RIGIDUS, Hall. 
Plate XI, figures 1-5. 
(G. rieipus, Hall: Geological Survey of Canada, Report for 1857, page 121.) 
Description.—Frond multibrachiate, composed of numerous slender 
branching stipes, equally disposed on the two sides of their origin. Radicle 
minute : funicle short, being a little more than one tenth of an inch in length, 
dividing at the two extremities, the divisions diverging at an angle of 115°; 
each stipe again bifurcating at least five times, following the principal axis, 
and occasionally six times in mature individuals ; the principal branches 
again bifurcate twice or three times before reaching their termination. 
In the first bifurcation of the stipe, (or second from the radicle, ) the angle 
of divergence is about 78°, and in the second about 60° ; while the succeeding 
divisions diverge at a less angle, and become somewhat curved. In one 
of the stipes beyond the first division (making one eighth of the entire 
frond) we are able to count fifteen bifurcations ; giving eighteen branchlets 
to a secondary division of the stipe; or 18 x 8, = 144 in an entire frond, 
if uniformly branched as in the one examined. 
Stipes and branches slender, cylindroid exteriorly, rigid, nearly uniform 
in width to the third bifurcation ; all the measurements from the base giving 
about four hundredths of an inch diameter upon the outer side or back of 
the branches. A single specimen, which is apparently the upper side of 
the stipe, is nearly twice as wide as the above, and preserves a part of the 
solid axis: this is replaced by iron pyrites. | 
None of the specimens exhibit well-defined cellules below the last bifur- 
cation, though some of the branches are obscurely undulating or denticu- 
late on one side ; but the specimens examimed do not admit of a satisfac- 
tory determination of these characters. 
The impossibility of tracing any evidence of cellules upon any part of 
the frond below the last bifurcations, suggests the possibility that this 
Species was not celluliferous except'at the extremities of the stipes or 
branches. In most of the specimens examined, these celluliferous parts 
have probably been broken off; since it is evident that the whole frond 
has been subjected to maceration, and even the stronger parts are often 
broken. The regularity of bifurcation is a remarkable feature, and fur- 
nishes a character by which even fragments of the species can be readily 
distinguished; smaller fragments may be known by their rigid wiry 
appearance. 
