GRAPTOLITES OF NEW VORK, PART 2 333 



a Dicranograptus spinifer var. geniculatus nov. 



Flate 23, figures 4-6 



The most striking of the forms of Dicranograptus is a variety of 1 ) . 

 s p i n i f e r which is characterized by (i) the stoutness of the branches, (2) 

 a flexure of the uniserial branches, (3) the extension of the mesial spines 

 over the entire or nearly entire biserial 

 portion of the rhabdosome. 



This variety is by its strongly fusiform 

 biserial portion and the extension of the 

 mesial spines close to the bifurcation nearer 

 related to the British representatives of 

 D . spinifer than to any other form. It 

 also has in common with the latter the 

 greater width of the biserial portion (2 mm) 

 and of the uniserial branches, which in some 

 specimens have a uniform width of 1.6 mm. 

 Also its spines are longer than those of our 

 other representatives of Dicranograptus and 

 the ventral walls of the thecae markedly 

 more convex. Its test is stronger than that 

 of the other species and varieties and it 

 seems to have been an altogether more 

 robust form. 



A similar flexure as that observed in 

 this variety had been noticed by Elles and 

 Wood in specimens of D. ramosus [oft. 

 cit. pi. 2b, fig. 6b], and a general tendency to 265 -6 7 Dicranograptu spinifer 



var. genie 11 latus nov. Figure 265 shows 



such a development has been observed in our ^ a f r if cter? of . b , iseri ^ p° rt .i°n- Figure 2 6<s, pan 



1 ot the uniserial portion of the same specimen ; 



. 1 r t\ r 1 r i figure 267, that of another. Glenmont, N. V. 



material ot D . ramos u s | see pi. 21, rig. 7 |. x s 



The above cited authors remark "should the discovery of more examples 

 prove that this latter form was a permanent one, it would be worth)' of a 

 varietal name." It is very probable that D. arkansasensis Gurley 



