328 NEW YORK STATE MUSEUM 



and Ami in the equivalent beds of the province of Quebec in Canada; and 

 Gurley lias also recorded it from the Dicellograptus zone in Arkansas. 



In Great Britain D. ramosus is, according to the monographers, by 

 no means so common as in the Normanskill shale of this State ; it is but 

 rarely found in the corresponding- Glenkiln shales and more frequently in 

 the following Lower Hartfell shales. It is there known from Scotland, 

 Wales and Ireland ; McCoy and T. S. Hall record the species also from the 

 province of Victoria, Australia. 



Remarks. The fragmentary rhabdosomes of graptolites, scattered pell 

 mell over the slabs, are liable to form very deceptive, though but accidental 

 groups. One of these has been mistaken by Hall for a more complete 

 rhabdosome and been figured \loc. cit. pi. 7$, fig. 3f] and described as "a 

 specimen branched below, and bifurcating above." The figure shows — 

 and the original leaves no doubt about it — that here two rhabdosomes 

 have come into such position that the sicular end of one has fallen upon 

 the point of bifurcation of the other, thereby giving the impression of a 

 continuous biserial portion with four uniserial brandies. Unfortunately 

 it is jut this figure that has entered into some of our textbocks of geology, 

 thereby perpetuating a misconception of one of our most striking Xormans- 

 kill graptolites. 



The sicular extremity of the rhabdosomes is not well shown in any of 

 the specimens; the most distinct of them is reproduced in figure 255. 

 It exhibits the virgella, the lateral spines and their position on the thecae ; 

 and the growth directions of the primary thecae. As far as the evidence of 

 this and another specimen goes, the origin of the first thecae in this species 

 is like that described for the whole genus 1))- Elles and \\ ood. The alter- 

 nate arrangement of the thecae does not seem to continue beyond the first 

 four thecae, for the sutural line of a dividing septum has been observed in 

 several specimens to begin directly above them. 



