572 NEW YORK S'TA'TK MUSEUM 



Etagraptus lentus, indicates quite distinctly the separate path of 

 the evolution of at least one of the thin biramous graptolites with very- 

 remote slender thecae. The family Leptograptidae appears hence to comprise 

 several entirely different evolutional series. We have for this reason 

 separated one of these as the Coenograptidae. 



Also the genera grouping themselves around Tenmograptus are very 

 liable to be found eventually to constitute a separate family, which is 

 characterized by peculiarities of branching. The New York fauna contains 

 only a single representative of the genus Temnograptus. 



The suborder Grraptoloidea Axonophora does not appear till the time of 

 the last of the zones, whose faunas have been here investigated, and it does 

 not attain its principal development till the late Lower Siluric and the Upper 

 Siluric. 



Freeh has separated the Climacograptidae from the Diplograptidae 

 Lapw. and referred the genus Retiograptus to the Climacograptidae. As 

 the direction of growth and shape of the thecae in Climacograptus are very 

 different from those found in Diplograptus, this separation seems well sup- 

 ported by the facts and is adopted here. 



With the Diplograptidae have here been united the genera Glosso- 

 graptus and Trigonograptus, the latter with some doubt arising from the 

 peculiar direction of the aperture, which is different from that of other 

 Diplograptidae. 



We thus obtain the systematic arrangement of the New York forms, 

 which is given in the following synoptic list of our species. 



SyTwptic list of fossils described 



Order 1 DENDROIDEA Nicholson 



Family DENr>ROGRA.E»TiDA.B Roemer 



Genus dendrograptus Hall 



Dendrograptus flexuosus £[all 

 D. (?) succulentus s^. nov. 

 D. fluitaus sj>. nov. 



Genus callograptus Hall 

 Callograptus salteri Jlall 

 C. cf. diffusus Jlall 



Genus ptilograptus Hall 

 Ptilograptus plumosus Hall 

 P. geinitzianus Jlall 

 P. tenuissimus sp. nov. 



