344 



NEW YORK STATE MUSEUM 



Diplograptus foliaceus T. S. Hall. Geol. Sur. Victoria Rec. 1904. v. 1, 



pt 3, p. 2 19 

 Diplograptus foliaceus Ami. Geol. Sur. Can. Sum. Rep't. 1905. p. 1 2 

 Diplograptus foliaceus T.S.Hall. Geol. Sur. Victoria Rec. 1906. v. 1, pt 4, 



P-275 



There is no form which is so common in the New York Trenton shales 

 and at the same time so perplexing by the variability of its aspects as 

 D. foliaceus. I therefore gladly avail myself of the opportunity of 

 giving here instead of my own observations, Lapworth's welcome descrip- 

 tion of the species and of its two Normanskill varieties, which is contained 

 in his manuscript report sent in 1890 to Dr Gurley. These descriptions 

 were based on a collection of Normanskill graptolites from Stockport, 

 Columbia co., N. Y. 



On D. foliaceus itself, Professor Lapworth has made the following 

 remarks : ' 



Of all the Diplograptidae there are none which are so difficult of sepa- 

 ration and determination as those which paleontologists are at present in 

 the habit of referring to D. foliaceus Murchison and its varieties ; or 

 to the associate and doubtfully separable ally D . r u g o s u s Emmons. 



They range in geological time from the horizon of D . pristini- 

 formis Hall, to that of D. quadrimucrpnatus, and curiously 

 enough exhibit all the characters intermediate between these two well 

 marked species. They all possess the same type of rhabdosome (polypary), 

 nemacaulus (virgula) and theca ; but differ extraordinarily among them- 

 selves as regards (1) size, (2) number of thecae, (3) degree of lateral ami 

 proximal ornamentation. 



The rhabdosome (polypary) in all of these forms is of the general 

 shape of a prism of quadrangular section, with rounded ends. ( The section 

 is about twice as broad from back to front as from side to side. ) The 

 proximal part of the rhabdosome (polypary) converges to an abrupt extrem- 

 ity, furnished with a radicle and two lateral spines ; but in the distal parts 

 the margins of the rhabdosome (polypary) are parallel. 



The nemacaulus (virgula) is remarkably stout, is marked often by a 

 central groove and is prolonged in antisicular direction (distally) to a length 

 somewhat less than that of the rhabdosome itself. A straight seam or 



1 For the sake of uniformitj of terminology the writer has inserted the terms used in 

 this memoir, wherever different ones were used, and added the latter in parentheses, 



