GRAPTOLITES OF NEW YORK, PART 2 20 I 



of the Normanskill shale of Mt Moreno, where it is associated with C 1 i- 

 macogr. parvus. It is also of frequent occurrence in the shale at 

 Speigletown, Rensselaer co., N Y. and has been observed in a few speci- 

 mens at Kenwood and in the collection from Stockport. At Kenwood 

 it is associated with Diplogr. foliaceus, Climacogr. parvus, 

 D i c r a n o g r. r a m o s u s and D i c e 1 1 o g r. m e n s u r a n s ; at Stockport 

 with C 1 i m a c o g r. p a r v u s and Dicellogr. s e x t a n s. 



Remarks. One could take the representatives of this type for the 

 central parts of rhabdosomes of N. ex i lis, whose secondary branches had 

 been stripped oft during their sinking to the bottom and I have no doubt 

 that the Stockport specimens have been included by Dr Gurley in N . 

 e x i 1 i s. The sicula and the proximal parts are nearly identical with those 

 of N. exilis and the main stipes similarly thin. But the numerous speci- 

 mens occurring together at Mt Moreno [see pi. 17, fig. 12] leave no doubt that 

 this form differs in constant characters from the similar N. exilis. The 

 principal ones are the greater and more uniform thinness of the main stipes 

 and branches, the different angle of divergence and the nearly straight form 

 of the main stipes. These characters combine to give the variety a habit 

 quite different from that of the typical species. 



Family dicranograptidae Lapworth 



DICELLOGRAPTUS HopkinSOll 



The forms for which Hopkinson erected the genus Dicellograptus in 

 1 87 1 had before been united with Didymograptus until, when the fact of 

 their different thecal form was recognized by Hall, they were brought under 

 Dicranograptus. From the last named genus they differ in the absence of the 

 biserial portion of the rhabdosome. On this basis the genus is character- 

 ized by the diverging of the two uniserial stipes or branches of the first 

 order directly from the sicula and the Dicranograptid type of the thecae. 



It is one of the most important genera of the Trenton shales of North 

 America — there are no less than 17 species and varieties of this group 

 described in this paper — indeed, it is so characteristic of these shales that 



