GRAPTOLITES OF NEW YORK, PART 1 



675 



Fl(?. 71 OidymoRraptus patulus 

 Hall sp. Young rhabdosome. Obverse 

 view. Deep kill, x 5.25 



Didymograptus patulus Elles & Wood. Monogr. Brit. Grapt. ptl. Pal. Soc. 



vol. for 1901. p.l3, pl.l, fig.8a-c 

 Didymograptus patulus Kuedemann. N. Y. State Paleontol. An. Eep't. 



1902. p.556 



Description. Primary disk large, subcircular, very tenuous [fig. 9]. 

 Nema very short (.3 mm) or absent [fig. 9]. Sicula inconspicuous, about 

 2 mm long. The first theca originates a little above the middle of the sicula, 

 the second near its aperture. The branches horizontal, nearly straight, 

 attaining a length of 5 cm and more, narrow in the proximal part (.7 mm), 

 but widening rather rapidly to a maximal width of 2.6 mm and narrowing 

 again at the growing end. Thecae numbering 

 10 to 12 in 10 mm, curved and inclined at 40° 

 in their proximal and 60° in their distal part, 

 four times as long as wide, in contact two 

 thirds to three fourths of their length. Outer 

 margin distinctly concave, apertural margin straight to slightly concave, 

 mucronate at the lower end, forming an angle of 40° to 50° with the axis 

 of the thecae. 



Position and localities. D. patulus is at the Deep kill very common 

 in graptolite beds 1 and 2, representing the Tetragraptus zone, but apparently 

 does not persist to the zone with D. b i f i d u s. Hall received his type from 

 the Quebec group at Point Levis. Gurley records it from the Main Point 

 Levis zone, which corresponds to our Tetragraptus zone. Ami does not 

 mention it in his list, but Matthew found it to be common in association 

 with D. n i t i d u 8 in division 3d of the St John group. 



In England other species have, as Lapworth, Elles and Wood assert, 

 been repeatedly mistaken for this type. According to these authors, it occurs 

 in the Lower Llanvirn beds of the St David's district in Wales, associated 

 with D. bifidus, D. nicholsoni, etc.; in the Middle and Upper 

 Arenig of the Shelve district in Shropshire ; and at Kiltrea near Ennisworthy 

 in Ireland. It appears, hence, in Great Bi-itain, to find its principal develop- 

 ment in a higher horizon than in Ameiir;i. In the Skiddaw slates it seems to 



