548 NEW YORK STATE MUSEUM 



graptus angustifolius indicate, no longer distinguishable ^vithin the 

 coalesced dorsal walls of the branches. 



h Phylogeny of the orders of graptoHtes. A problem not yet solved is 

 the relation of the Dendroidea to the Graptoloidea. Freeh considers the 

 Dendrograptidi a part of the Axonolipa. In fact, they lack the support- 

 ing rod of the Axonophora, and their thecae are directed distally, while 

 the sicula holds a proximal position. But they differ so greatly, not only 

 in general appearance of the mature colonies, but also in the composition 

 of the branches, from all other graptolites, that the question is pertinent, 

 whether they should not be considered a separate order for themselves, 

 specially as they also continue to coexist with, or rather persist beyond, all 

 other graptolites. 



It is here, however, not to be forgotten that several authors have 

 recently been not disinclined to consider the Graptoloidea as derived from the 

 Dendroidea. Thus Wiman [1893, p.35] has pointed out that a fragment of a 

 dendroid is often externally undistinguishable from a fragment of a grap- 

 toloid, and suggested that the rhabdosomes of Graptoloidea ma}- be but 

 the external periderm of those of Dendroidea, and that in the former the 

 delicate tubes (his " gonangia " and " budding individuals") filling the com- 

 mon canal of the Dendroidea, which also in these are rarely retained, 

 may have been so thin walled that they never, or only in most excep- 

 tional cases, left any traces of their former existence. He adduces in this 

 connection an observation of Hopkinson [1882, p.56], Avbo observed in 

 T e t r a g r a p t u s s e i- r a and I) i d }' m o g r a p t u s e x t e n s u s, partitions 

 between the proximal parts of the thecae and the common canal, which sepa- 

 rate the latter by transverse septa into sj)aces corresponding to the thecae. No 

 traces of these partition walls have been found by the writer in sections of 

 pyritized specimens of several Dichograptidae, and it seems possible that the 

 appearance of the partitions has been produced by cutting through the 

 proximal parts oi the thecae in somewhat obliquely embedded material. 

 How-ever this may be, it is to be conceded that the failure to observe the 

 •delicate tubes within the Graptoloidea, with the restricted number of observa- 



