GRAPTOLITES OF NEW YORK, PART 1 687 



There occur in the uppermost part of graptolite bed 2, belonging to the 

 Tetragraptus zone, very minute and delicate rhabdosomes of a type of the 

 declined group of Didymograptus, which is sufficiently close in its specific 

 characters to a species described by Tullberg to warrant identification with it. 



Description. The sicula is small (1 mm) and narrow. The first and 

 second theoae branch out at different distances from the apex of the sicula. 

 The rhabdosome is hence distinctly unsyrametric regarding the origin of the 

 branches. The latter are rather short, if complete and of uniform width (not 

 exceeding .25 ram). The largest branch measures only 3.2 mm in length. 

 The angle of divergence between the two branches is about 60° to 80° ; in 

 one specimen 110°, probably by oblique compression. The thecae are very 

 slender, tubular, hardly widening, numbering 8 in 10 mm, inclined at only 

 10° to 15° and overlapping not more than one quarter of their length. The 

 outer walls and the apertural margins are straight; and the angle which 

 the latter form with the axis of the branch is 90° or more. 



These characters, which are constant in about half a dozen specimens, 

 differ slightly from the original description of Tullberg, who observed an 

 inclination of the thecae of about 30°. But Tullberg's figures show an angle 

 of inclination not larger than the one observed in the Deep kill specimens, and 

 the English specimens furnished also a smaller angle. 



Position and localities. It has been collected in the uppermost part of 

 graptolite bed 2 (Tetragi-aptus zone), associated with the sicula of all the 

 other species, Avith which it probably settled at the same time on account of 

 its similar weight and size. A few specimens were also observed in the beds 

 with Diplograptus dentatus at Mt Moreno near Hudson N. Y. The 

 range of this species is hence considerable. Tullberg obtained the type of 

 the species from the lower Graptolite shales of Kiviks-Esperod in Scania, and 

 cites it later (1882) as a form of the Tetragraptus zone of Scania. Tornquist 

 found it at Mossebo in Westrogothia ; and Brogger in Etage 3b (Phyllograptus- 

 schiefer) at Krekling in Norway. Elles and Wood recoi-d that their material 

 has been collected in the Arenig rocks of Bennane Head near Ballantrae, 

 Scotland. 



