70(1 NEW YORK STATE MUSEUM 



Holm states that no virgula "has been observed [1895, p,489] ; while 

 Elles reports [1896, p.494] having seen one in a specimen of P. anna 

 passing from the apical end of the sicula the full length of the rhabdo- 

 some. The liomology of the structure with that of Tetragraptus 

 s i m i 1 i s argues certainly for the, at least temporary, suspension of the sicula 

 from a primary disk by means of a nema. Corresponding to the growth of 

 the four branches in a proximal (or backward) direction this nema must have 

 become inclosed into the rhabdosome, analogous as in Diplograptus. If it 

 then is sometimes absent, as Holmes observation in P. angustifolius 

 would tend to show, it must have been received so intimately into one of 

 the periderraal walls, that it is no longer distinguishable as a separate body, 

 which is the more possible, as it is anyway an extremely slender and delicate 

 thread in most Dichograptidae. 



It is, however, a peculiar fact that among the very great number of 

 well preserved specimens found in the Ne^v York shales not a single one has 

 been observed with any trace of a nema protruding from the antisicular 

 end of the rhabdosome. Nor do I iind any suggestion in either the 

 descriptions or the figures of other material indicating that such an organ 

 has ever been noticed. Yet it is necessary to postulate the suspension of the 

 colony from the ascending growth directions of the branches as well as of 

 the thecae. The appendages, which were observed by Hall, in P. typus, 

 and termed "radicles" are sicular spines and, therefore, found at the oppo- 

 site free end of the rhabdosome. While we have not noticed them in our 

 material of P . typus, they were found to be well developed in P . anna 

 [pi. 15, fig. 2 3] and in P. ilicifolius. 



The phylogeny of the group has been touched in the introduction 



[p.563]. 



Phyllograptus ilicifolius Hall 



Plate 15, figures 15-22 



Phyllograptus ilicifolius Hall. Canadian Organic Remains, decade 2. 



1865. p.I21, pL16, fig.1-10 

 Cf. Phyllograptus ilicifolius var. grand is Elles. Quar. Jour. Gaol. See. 



1898. 54:493 



