GRAPTOLITES OF NEW YORK, PART 1 583 



Position and localities. Rai-e in graptolite bed 2 of the Deep kill 

 section, belonging to the Tetragraptus horizon. 



Memarhs. Only incomplete rhabdosomes have been observed. These 

 suggest a form similar in its habit to Hall's D. flexuosus from the 

 Levis beds of Quebec. The latter type bifurcates, however, more frequently 

 and regularly, and has thecae arranged less closely by one fourth and 

 differently shaped, with more obtuse apertural processes and angles. 

 In the corresponding Skiddaw horizon no Dendrograptus has been found. 



cALLOGRAPTus Hall. 1863 



Since the erection and definition of the genus Callograptus by Hall 

 in his work, the Graptolites of the Quebec Grotip, very little has been added 

 to his observations on the genus. This is largely due to the fact that no 

 more representatives of the same have been found, with the exception of 

 two new species recorded by Hopkinson and Lapworth from Ramse}- 

 island [1875]. 



Hall based his genus mainly on its mode of branching and the resulting 

 aspect of the rhabdosome ; stating that it has " numerous slender bifurcat- 

 ing branches proceeding from a strong stem or axis," and that in its aspect 

 it is intermediate between Dictyonema and some forms of Dendrograptus; 

 that the branches are sometimes distantly and irregularly united by trans- 

 verse dissepiments, but that the frond has not the regular, reticulate structure 

 of Dictyonema and differs from Dendrograptus in the mode of branching and 

 the form of the thecae. 



The microscopic investigations of Wiman, which have resulted in the 

 demonstration of the composite character of the thecal structures of both 

 Dictyonema and Dendrograptus, have for lack of suitable material not been 

 extended to this genus, and its actual relations to either Dictyonema or 

 Dendrograptus are still unknown. Hall's material did not permit him to 

 determine the character of the thecae, the latter appearing as simple oval 

 impressions on the surface of the compressed branches. 



While the shale material of the Deep kill is not suited for an elucidation 

 of the internal structure of the branches, the observation of smaller pores 



