NEW YORK STATE MUSEUM 



that varies from 25 to 8o°, probably in consequence of oblique compression, 

 but in the majority of specimens lies between 40 and 6o°. The branches 

 are frequently straight, but mostly gently curved, either first concave and 

 then convex, or convex from beginning", so as to reapproach distally. The 

 biserial section begins narrow (initial width .7 mm) but widens to 1.7 mm ; 

 the uniserial branches are uniformly 1 mm thick, in some long branches 

 widening gradually to 1.2 mm. 



The sicula measures 1 to 1.1 mm, and is furnished with a short virgella. 

 From its apical end a dividing septum proceeds, and only the first four 

 thecae grow alternately. The biserial section consists of 5 to 6 thecae, 



■42 Dicranograptus nicholsoni Hopkinson. Fig. 230 _ Biserial portion of .1 rhabdosome showing 

 septum. From the Utica shale of the Mohawk valley (original in National Museum). Fig. 240 Frag- 

 the Utica shale of Cincinnati (original in Ulrich collection). Fig. 241, 242 Portions of specimens from the 



of Saratoga lake. Figure 241 shows distinctly the sicula and septum. Figure 242 shows the profile view of 



• " 5 



mostly 5, on either side (8 in the Cincinnati specimens). The thecae num- 

 ber mostly 10 in 10 mm (9-13 in 10 mm); they have convex outer walls, 

 which in the biserial section are furnished with strong mesial spines ; they 

 overlap about one half their length (the latter, in the later thecae, is 2 mm) ; 

 their apertural parts are introverted and introtorted and contained in or 

 almost filling round excavations that occupy fully one third or more of the 

 width of the branch. 



Position and localities. 1). nicholsoni occurs in mutations [see 



