GRAPTOLITES OF NEW YORK. PART 2 



i D 5 



an initial width of i mm to a maximum width of 2.5 which is attained in a 

 distance of 15 mm from the sicular extremity and then maintained. Sicula 

 not observed. Sicular extremity furnished with a short blunt virerella 

 (about .4. mm long) and two equally short straight lateral spines. Thecae 

 numbering 11 to 13 in 10 mm (30-32 in 1 inch), inclined at an angle of 

 30"-40'\ overlapping a little more than one third, the outer margin dis- 

 tinctly convex with the proximal part frequently slightly concave, 'r^n 

 The aperture horizontal, concave, the interthecal excavation about 

 one fourth the width. Nemacaulus very thin and inconspicuous 

 within the rhabclosome and not seen protruding' beyond vgv 

 the antisicular end. 



Position and locality. In the transition beds at Van ^^ ':;> 

 Schaick island (with Cryptogr. tricornis), in the 

 Utica and Lorraine shales of the Hudson, Mohawk and 

 Black river regions. 



Remarks. This mutation of I), folia- 

 ceus is in the form of the rhabclosome and the 

 form and close arrangement of the thecae most 

 nearly related to D. f o 1 i a c e u s var. a c u t u s 

 and quite evidently a direct descendant of the 

 same. It is the last representative of the group 

 of D. foliaceus in our rocks and persists ^| 

 into the Lorraine beds. In the beds at Van 



Fig. 296-98 Diplograptus foliaceus 



Schaick island, which may be properly referable ^^tll^v^yJ^tJ^ 



__. 1t ... (Ward's lane), (x c) 1' ig. 298 Enlargement 



tO the Upper DlCCllOgraptUS ZOne, It IS the mOSt (xs)ofoneoftherhabdosomesirithegroup, 



11 ° L reproduced by Hall in plate 72, figure 1a 



common graptolite and there it attains its maxi- 

 mum size [296]. In smaller individuals it fills layers of the Utica shale, as 

 in the neighborhood of Amsterdam in the Mohawk valley. It further 

 occurs in the uppermost Utica beds around Albany, as at Ward's lane, Black 

 rock, etc. and in the Lorraine beds, whence Hall's type of D . prist is 

 [pi. 72, fig. 1 a, ib=298 which typically represents this mutation] came. The 

 gradual widening of the rhabdosome, the small size of the denticles and 



