386 CANADIAN FOSSILS. 
The development of the diprionidian forms, as deduced from the young 
graptolites which we find associated with the reproductive cell-bearing 
stipes, would show that these forms of graptolites exist as single and 
simple independent stipes from the commencement of their growth. 
Nevertheless I conceive that both Retiolites and Retiograptus may have 
existed in compound fronds, having their origin from a central point not 
unlike in the commencement to Graptolithus Logani, but without the 
central disc. These fronds were probably concavo-convex, as were the 
individual stipes. The solid axis, instead of being central, is placed exter- 
nally along the centre of the convex or outer side ; and the cell-divisions 
on that side reach to and join it; while on the upper or concave side the 
cell-divisions do not reach the centre, leaving a space for the common 
body, which has been shown by Barrande and Geinitz to produce a central 
longitudinal prominence. 
In these forms the mode of development has been similar to that already 
explained, the modification being chiefly in the external position of the 
axis and the joining of cell-divisions with the axis on one side; leaving 
the common body in a somewhat triangular form, from which the alveoles 
are developed on either side. 
Fig. 30. Fig 31. 
% 
GraproLtitHus WHITFIELDI: 
DEDALY 
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eV UVVEUYYTIVIFT ESD eF 7 
SSAA Sexes 
yx 
GRAPTOLITHUS PRISTIS: 
enlarged. enlarged. 
