GRAPTOLITES OF NEW YORK, PART 2 25 1 



river in British Columbia ; in all of these places in the same horizon (Dicel- 

 lograptus zone) as at the Normanskill, with the exception perhaps of the 

 last mentioned locality. 



Ren/arks. No other species of Didymograptus to which this gigantic 

 form could be compared occurs in the Trenton shales. It is certainly a 

 peculiar fact that a form attaining such relatively immense length and width 

 should still appear at the very close of the hemera of the genus. 



Hall has compared a considerably older and smaller form ( D . s i m i 1 i s 

 from the Quebec and Deepkill shales, see Mem. 7, p. 677) with this species 

 and a comparison of the measurements emphasizes still more the similarity 

 of their thecal form. 



Didymograptus serratulus (Hall) 



Phite 13, figure 4 



Graptoli thus serratulus Hall. Pal. N. Y. 1847. 1: 274; pi. 74, fig. 5a, b 



Gr apt oli thus serratulus Walcott. Alb. Inst. Trans. v. 10. 1883. (Advance 



sheet. 1879. p. 35) 

 Graptoli thus serratulus Hall. N. Y. State Cab. Nat. Hist. 20th Rep't. 1867. 



p.22 3 f 

 ? G r a p t o 1 i t h u s (Monograptus) serratulus Whitfield. U. S. Geog. Sur. 100th 



Mer. Lieut. Wheeler's Rep't. 1877. 4: 19 

 Didymograptus serratulus Walcott. Geol. Soc. Am. Bui. 1890. 1 : 338 

 Didymograptus serratulus Gurley. Geol. Sur. Ark. An. Rep't. 1892. 3:411 

 Didymograpsus serratulus Gurley. Jour. Geol. 1896. 4:295 

 D id y in ograptus serratulus Roemer &: Freeh. Lethaea pal. 1897. 1 : 589 

 Didymograptus serratulus Ruedemann. N. Y. State Mus. Bui. 42. 1901. p. 497, 



54i 

 Didymograptus serratulus Elles & Wood. Monogr. Brit. Grapt. pt 1. (in Pal. 



Soc. 1901). p. 29; pi. 2, fig. 7a, b 

 Non Didymograpsus serratulus Nicholson. Geol. Soc. Quar. Jour. 1868. 



24: 136 

 Non Didymograpsus serratulus Nicholson. Ann. & Mag. Nat. Hist. Ser. 4, 



v. 5. 1870. p. 343; pi. 7, fig. 3, 3d 



Description. Rhabdosome consisting of two straight or gently convex 

 branches, which inclose an angle of i40°-i55° (typically 140 ), attain a 

 length of 8+ cm, gradually broaden from .5 mm to 1.2 mm. Sicula long 



