720 NEW YORK STATE MUSET'M 



the rhabdosome as mucli as 12. In normal specimens they appear as subacute 

 denticulations, are narrow, forming an angle with the axis not greater than 

 20°, are free for one thi^-d of their length, and possess a slightly concave outer 

 margin, slightly mucronate or acute apertural extension, straight or slightly 

 concave apertural margin, which forms an angle of 80° to 90° with the axis. 

 There are however other specimens in which the outer margins are strongly 

 rounded, the apertural margin is straight or slightly convex, and some in 



which the thecae appear to be free for at least one 

 half or even two thirds of their length. 



The virgula which is often seen to extend through 

 the rhabdosome is straight and distinct, but apparently 

 not so strong as indicated by Hall's figure. A strong 

 median sicular spine, about 5 mm long, has been 

 observed in several specimens, as well as two short 



Fig. 100 Diplograptusi.T • -i 



(lentatus Brongniart sp. lateral SpiUUlCS. 

 Fragment of middle portion 



atpec?s''o°rttilcal.''°rshhiii Fositwu and localities. This is the most char- 



qiiaiTv at Mt Moreno. x5 . . , t i» i i i • 



acteristic and common graptolite or the last horizon 

 in the Deep kill section and is there restricted to the same. It occurs ^vith 

 equal frequency in the some^vhat older bed at Mt Moreno, near Hudson. 

 In. Canada it is found in the horaotaxial Point Levis zone. Gurley records 

 it from Arkansas. In the Upper Skiddaw slates (Ellergill beds) it has been 

 observed in many localities. Hopkinson and Lapworth I'eport it also from 

 the Upper Arenig of Ramsey island and the Llanvirn quarry in Wales. In 

 Sweden it has been found at the top of the Phyllograptus zone (subzone 

 with P h y 1 1 ( ) g r a p t u s cf . t y p u s ) . 



Itemarhs. The great variety of appearances as well as of dimensions 

 of this species has been commented on by Hopkinson and Lapworth, and 

 Elles. It is also very noticeable in the Deep kill material and still more 

 so in that from the Mt Moreno, which contains numerous specimens that 

 attain a width of 2.6 mm — thus surpassing considerably the maximal width 

 observed by jNIiss Elles — and have not more than nine thecae in the 

 space of 10 mm. These specimens differ so materially from the originals of 



