334 NEW V0RK STATE MUSEUM 



from the Dicellograptus zone of Arkansas [see p. 329] is identical with the 

 variety of D. ramosus here referred to. The British geniculate form 

 being nonspinose, it represents a parallel development in D. ramosus 

 to that here observed in D . s p i n i f e r. 



In the extreme forms [see pi. 23, fig. 4] the branches become horizontal 

 after the bifurcation, and resume afterwards by an almost rectangular flexure 

 a direction corresponding to that of the branches in the main species. 



Position and localities. This variety has been mainly observed in the 

 Normanskill shale at Glenmont, N. Y., associated with Climacogr. 

 parvus, Lasiogr. mucronatus and Dicellogr. gurleyi and 

 in one specimen also at Mt Moreno in association with Diplogr. foli- 

 aceus, Climacogr. bicornis and Dicellogr. sextans. 



Dicranograptus furcatus (Hall) 



Plate 23, figure 7 



Graptolithus furcatus Hall. Pal. N. Y. 1847. 1:273; pi. 74, fig. 4a-f 

 Dicranograptus furcatus Hall. Can. Org. Rem. Dec. 2. 1865. p.15 ff, et al. 

 Dicranograptus furcatus Lapworth. Ann. & Mag. Nat. Hist. 1880. 5:283 

 Dicranograptus furcatus Walcott. Alb. Inst. Trans, v. 10. 1883 (Advance 



sheet. 1879. p. 34) 

 Dichograptus furcatus Whitfield. Am. Jour. Sci. Ser. 3. 1883. 26:380 

 Dicranograptus furcatus Walcott. Geol. Soc. Bull. 1890. 1:339 

 Dicranograptus furcatus Gurley. Jour. Geol. 1896. 4:297 

 Dicranograptus nicholsoni Freeh. Lethaea Pal. 1897. 1 : 617, fig. 181 



Description. Rhabdosome of medium size, consisting of a short biserial 

 portion (2.3-2.5 mm long, 1 mm wide, and composed of eight thecae) and 

 two uniserial branches, which grow upward in oppositely directed spirals, 

 forming in the compressed condition a series of successive elliptic loops 

 and diverging at the point of bifurcation at an angle of 40° to 90 (in com- 

 pressed state). The width of the brandies is uniform in every specimen, 

 with variations from .9 to 1.1 in different individuals. The sicular extremity 

 is squarish, provided with a small virgella and inconspicuous lateral spines. 

 The sicula is short and blunt, about .8 mm long; the first two thecae grow 

 horizontally outward and then turn abruptly upward. The thecae are short 



