SUPPLEMENT. 



Sll 



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 wliich 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 thtre 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-forra 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 Kastrites 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 flgurod in Emmons's American Geology, Plate 1, 

 new Genus Nemaokaptcs, is evidently a fragment of G. gracilit. 



;. 6, and described as the type of a 



