720 NEW YORK STATK MI'SET'Jf 



the rhabdosome as much as 12. In normal specimens they appear as subaciite 



denticnlations, are nar^•o^v, 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" ^vith the axis. 



There are liowever 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 



^^|F half or even two thirds of their length. 



IJ^^L The virgula which is often seen to extend through 



S^^b^ the rhabdosome is straight and distinct, but apparently 



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



^^^t, median sicular spine, about 5 mm long, has been 



^1^^ observed in several specimens, as Avell as t\vo short 



lien tat us Brongniart sp. lateral SpinuleS. 

 Fragment of middle portion 



Ii'9P^troTthlcal'.''"Alhhiii Poftition and localities. This is the most char- 



quarry at Mt Moreno. x5 . . -, , . i> , i i . i • 



acteristic and cc^mmon graptolite oi the last horizon 

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

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

 In. Canada it is found in the homotaxial 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 quarr}- in Wales. In 

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

 with Pliyll ograp.tiis cf. typus). 



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

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

 Elles. It is also very noticeable in the Deej) 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 Miss Elles — and have not more than nine thecae in the 

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



