580 NEW YORK STATE MUSEUM 



Hall's types came from a coarse, greenish shale at Point Levis, in 

 which it is associated with Tetragraptus serra, Phyllpgraptus 

 t y p u s and Dendrograptus fruticosus. It may, hence, hold 

 there the same position as at the Deep kill. Lapworth, Gurley and 

 Ami did not observe it among the Canadian forms; data as to its exact 

 horizon can not therefore be obtained from their lists. Hopkinson and 

 Lapworth record it from their Lower Arenig of the Road Uchaf, Ramsey island 

 and the Middle Arenig of Whitesand bay. 



Remarhs. From the mode of compression of certain specimens [fig.6], 

 in which the branches are more crowded toward the marginal portions of 

 the frond, and from the more or less circular disposition of the branches 

 around the center in others, it would appear that the rhabdosome 

 did not always lie fanlike in one plane, but may have grown 

 infundibuliform. 



This species is characterized by the numerous and close bifurcations 

 and the greater divergence of the proximal parts of the divisions when 

 compared with the more distal ones, a feature which becomes still more 

 accentuated in D . d i v e r g e n s . Separated fragments of the rhabdosome 

 offer quite varying aspects according to their original distance from the 

 base. Very delicate fronds have been observed [fig. 7 and 8] in which 

 the branching is very close and the thecae also very closely arranged (as 

 many as 14 in 10mm), while iu other features they do not differ from 

 coarser fragments of the basal portions. As a quite perfect specimen, 

 figured by Hopkinson and Lapworth [fig.3b, ihid.'] shows the rhabdosome 

 to divide distally into a mass of closely arranged delicate branches, these 

 finer branched fronds have here been directly united with the coarser and 

 broader branches in the same species. 



A still more striking contrast between broad, short, basal branches 

 and rather abruptly dividing tufts of finer branches, was observed in a 

 new species from the horizon with Diplograptus dentatus, viz 

 D . (?) s u c c u 1 e n t u s . 



The great difference in the remoteness of the thecae between diffei'ent 

 portions of the rhabdosome is shown in figure 9. 



