(iKArTOLlTES OF .NEW YORK, L'AKT 1 (585 



Position and locality. In the shales with D i p 1 o g i a p t u s d e ii t a t ii s 

 at Mt Moreno near Hudson. 



Remai'l's. This species is nearest related to D . a c ii t i d e n s Lap- 

 worth, of which it presents the characteristic 

 features in a furtlier developed stage. As it also 

 succeeds the latter in o-eoloa-ic time, it may well Fig- sn Didymograptus cuspi- 



O Cri ' J ciatus sp. nov. I'l-iiKmentot branch. 



-, .1 1 -I ^ , i> • 1 Ti -\'cv Ashbill quarrv at Jit Moreno. .\") 



be considered as a descendant oi it. it diners 



from D . a c II t i d e n s most markedl}^ in the prominence of the apertural 

 portion of the thecae, Avhicli in most thecae appears cuspidat(^ instead of 

 acutely dentate, as in D. acu tide lis. This is due to a widening, often 

 somewhat abrupt, of the thecae in their last growth stage. 



Didymograptus nicholsoni Lapworth 

 var. planus EUes &, Wood 



Plate 13, figures 10-14 



Didymograptus nicholsoni var. planus Elles & Wood. Monogr. Brit. 

 Grapt. ptl. Pal. Soc. vol. for 1901. p.29, pl.2, fig.5a, b 



Descrijption. Primary disk and nema unknown. Siciila small (about 

 1.6 mm long), relatively broad. Branches straight, or ^^ery slightly curved, of 



rigid appearance, both together forming a straight 

 line (angle of divergence 180°) ; short (maximal 

 length observed 28 mm) ; narrow, of nearly uniform 

 nf2^h•o'U?^L^|r.?a;^^pVa- width (about 1.1mm) after the sixth theca (width 



n u s E. i: W. Proximal portion 



Deep'ki'i'i."''' "^^'e-^^e v'ew. in proximal part ,5 mm). Thecae numbering 10 to 



11 in 10 mm, narrow, four times as long as wide, 



inclined at 20", in contact 



for but one fourth to <, ^. ^ - - ^ ^^i?*^ . ^. , , 



one third of their lensth. Fig. 82 Didymograptus nicholsoni Lapw. mr. planus 



o E. & W. Fragment of branch. Deep kill. x7 



Outer margins straight. 



Apertural margins slightly concave, normal on axis of theca ; two thirds the 



width of the branch. 



