GRAPTOLITES OF NEW YORK, PART 2 



30I 



Pi- 4, 



Dicellograptus divaricatus Hall var. rigidus Lapworth 



Dicellograp tu s divaricatus Lapworth. Cat. West. Scott. Foss. 1876. 



fig. 86 

 D i c el 1 o g r a p t u s m offatensis var. divaricatus Lapworth. Belfast Nat. Field 



Club. Rep't & Proc. v. 1, pt 4. 1877. apx. p. 141; pi. 7, fig. io 

 D i c el 1 g r a p t u s d i v a r icatus var. r i gi d u s Lapworth. Ann. & Mag. Nat. Hist. 



Ser. 5, v. 5. 1880. p. 163; pi. 5, fig. 20 

 Dicellograptus rigidus Gurley. Geol. Stir. Ark. An. Rep't. 1890. 3:416 

 Dicellograptus rigidus Gurley. Jour. Geol. 1896. 4:297 

 Dicellograptus divaricatus var. rigidus Elles & Wood. Monogr. Brit. Grapt. 



(Pal. Soc. 1904.) p. 144, fig. 88a; pi. 20, fig. 6a-e 



This remarkable variety has been described by Dr Gurley from 

 Arkansas as follows : 



This species resembles in angle of divergence 

 and oreneral outlines D. divaricatus Hall, but 

 may be readily distinguished from that species by the 

 great thickness of the branches (about 1.5 mm or 

 lib inch) and especially by the uniformity of the 

 thickness throughout the whole length. This form 

 also differs markedly from Professor Hall's species in 

 character of the base, which is much wider, stouter 

 and more rounded. Hydrothecae about 9 in the 

 space of 10 mm (22 to the inch). The Arkansas 

 form agrees closely with the diagnosis given by Pro- 

 fessor Lapworth for his var. rigidus. As he 

 suggests, this form is entirely distinct from D . 

 divaricatus. 



Horizon and locality. Dicellograptus zone 

 locality no. 32. 



We insert here a drawing of the best Arkansas 



specimen, made under Dr Gurley's supervision. As 



in the British variety the sicular part possesses a small peridermal film or 



"web," extended between the dorsal sides of the branches. This gives to it 



a thickened appearance. The thecae are not well shown in any of the 



Fig. 220 Dicellograptus di- 

 varicatus var. rigidus Lap- 

 worth. Rhabdosome from Arkansas. 

 Nat. size 



specimens. 



