GRAPTOLITES OF NEW YORK, PART 1 633 



it can not be deduced from his Avork vvbether it occurs there in the lower 

 or upper zone. Gurley, however, has observed it only among the grapto- 

 lites of the upper Levis zone, hence at the horizon where it occurs in entire 

 rhabdosomes at the Deep kill. Ami records it only from the island of 

 Orleans, in an association insufficient for exact determination of the horizon. 

 Matthew found it in division 8d of the St John group in Ncav Brunswick. 

 Nicholson, and Elles and Wood have described it from tlie Middle Skid- 

 daw slates, which correspond to the Wo lower zones of the Deep kill ; while 

 in the latter place, as in Canada, it may be restricted to a higher zone, the 

 Ellergill beds of north England. In Scandinavia it is represented by 

 Dichograptus kjerulfi Herm., occurring in the lower Phyllograptus 

 shales ; and in Australia it has been recognized b}' McCoy among the 

 graptolites of Castlemaine and other localities of the province of Victoria 

 (described as a variety, characterized by wider brandies and more robust 

 thecae). 



Remarlcs. The variability of the number of the branches of the last 

 order in this species and its bearing on the phylogeny of the Dicho- 

 graptidae have been discussed elsewhere. One of the stages, leading from 

 L. logani to Dichograptus octobrachiatus, in Avhich the 

 number of branches had been at least locally fixed, is that I'epresented 

 by Dichograptus kjerulfi, which has not more than 12 

 branches. 



In the Deep kill section the species rises a zone higher than in the other 

 localities, from which it has been known. But these stragglers have the 

 appearance of epacmic mutations of the species. One [pi. 9, fig.5] is so 

 reduced in all its dimensions, that I first thought it to be a new species, 

 but now consider it more appropriate to distinguish it as a mutation, viz 

 L . logani mut. p e r t e n u i s . This is characterized by extremely thin 

 branches (in lateral view but . 6 mm wide, in dorsal view . 25 mm), very short 

 thecae, numbering 10 to 12 in 10 mm, and inclined at the same angle as in the 

 type of the species. 



