SUPPLEMENT. 
.711 
been able to discover any extension of these parts, or evidence of a third or fourth 
main branch or stipe. Although it is not possible at the present time to determine 
fully the mode of growth, and the original form of this species when entire, we are 
nevertheless able to offer some additional information which may be of interest. 
In the minute forms which appear to be the young of this species, no lateral 
branches are developed, while the centre or base is marked by a transverse bar 
which extends almost equally on either side of the stipe or rachis. The accompany¬ 
ing figures 1-4 are illustrations of this form, which are enlarged to twice the 
natural size, fig. 1 presenting the animal in its earliest observed stage of develop¬ 
ment. 
The second step in the progress of development, which has been observed, is 
shown in fig. 2, which is from a very beautiful specimen in the collection of Mr. 
R. P. Whitfield : in this one, the general form is similar to that of fig. 1, but it is 
somewhat larger, and there are five lateral branches on each side. Another indivi¬ 
dual, somewhat farther advanced, presents eight or nine branchlets on either side, 
as shown in fig. 3. 
Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. 
At the same time it is not easy to see at once how this form should assume the 
S-form so common in the specimens observed, and consequently it is difficult to 
illustrate every stage of the process. We do observe, however, that the main stipes 
become more curved as they progress; and it is only necessary to spread out, on a 
flat surface, these two stipes in opposite directions and rectangularly to the direc¬ 
tion of the small branches, and we should have a form approaching that in which 
these fossils usually occur. 
The small specimen which I had referred to Rastrites in my communication 
to the Regents’ Report, is simply one half of one of those young individuals of G. 
gracilis , where the young branches are thickened and not distinctly serrate ( fig. 4)*. 
In the original specimen of G. gracilis there is a slight interruption in the con¬ 
tinuity of the main stipe, as is observed in many individuals of that form ; and 
* The specimen figured in Emmons’s American Geology, Plate 1, fig. 6, and described as the type of a 
new Genus Nemagraptus, is evidently a fragment of G. gracilis. 
