GRAPTOLITES OF NEW YORK, PART 2 



! 99 



The two forms figured by Professor Mall have been regarded by some 

 as separate species and I held this view until after I had examined a large 

 series lor the purpose of defining the supposed two species. 1 was however 

 unable to find any characters upon which to base a distinction. From the 

 forms represented by Professor Hall's upper figure [fig. 212) characterized 

 by a narrower angle with rigid branches straight from their origin and more 

 rapidly increasing in thickness, to those characterized by a larger angle 

 (which moreover is increased a short distance from the base by the curving 

 of the branches away from each other) and more slender branches, every 

 gradation occurs. 



We have not been able to find these gradations in the Stockport mate- 

 rial and observing in the collection from Glenmont still more extreme 

 forms [see pi. 18, fig. 7], which however preserve a certain uniformity among 

 themselves in different layers, we have deemed it necessary to distinguish 

 these as varieties, the aforegiven description being drawn 

 wide enough to comprise all of them. As the typical 

 form we will consider that selected by Lap worth, Elles 

 and Wood. This [see pi. 18, fig. 3] has a large angle of 

 divergence (270 and more) and nearly straight and 

 rapidly widening branches. It is the most common 

 representative of the species at Stockport. 



\ 



Fig. 215 li i ee 1 1 ograp t u s divaricatus var. rectus mov. Enlargement (x 5) of original of plate iS, figure 7 (type of variety) 



Dicellograptus divaricatus Hall var. rectus no v. 



Plate 18, figure y 



A distinct variety is that represented by figure 215. This has also 

 straight and steadily widening branches which, however, diverge at a greatly 



