718 NEW YOUK STATE MUSEUM 



Position and locality. Zone with Diplograptus dentatus at 

 the Deep kill. 



Memarhs. Similar strands of long, fine threads occur also in the two 

 subjacent horizons. They belong to another species, as suggested by the 

 smaller Avidth of the fibers, if they are at all congeneric with this fossil, for 

 no thecal apertures have as yet been discerned on them. 



Suborder B graptoloidea axonophora Freeh 



Family diplograptidae Lapworth 



DIPLOGRAPTUS McCoy. 1854 



The genus Diplograptus makes its first appearance in the uppermost 

 of the graptolite beds of the Deep kill (graptolite bed 6, horizon with 

 D. dentatus) and does not attain the acme of its development till the 

 Trenton period. We shall, for this reason, reserve the more detailed charac- 

 terization and discussion of this genus for the next memoir, which will contain 

 the descriptions of the graptolitea of Trenton and later age, and mention here 

 provisionally only a few of the most important facts. 



The genus was originally proposed by McCoy in place of Barrande's 

 Diprion, a name which was preoccupied. Like Barrande's term, it was 

 intended to include all forms with two series of thecae. By the separation of 

 several groups of biserrate forms as genera, as Climacograptus and Glosso- 

 graptus, the genus has been restricted to diprionid forms with a straight vir- 

 gula, inclined thecae and normal, mucronate or nonmucronate apertures. The 

 various forms com]irised by this definition have since been subdivided by 

 Lapworth [1873J, and Freeh has proposed [1897] a division into two groups 

 according to the presence or absence of apertural spines. 



The four species described here, viz D. dentatus, longicauda- 

 tus, laxus and inutilis, are evidently to be referred to Diplograptus 

 proper. 



It has been demonstrated by the present writer that the rhabdosomes of 

 Diplograptus are parts of a person of a higher order (synrhabdosome), they 



