Clio 



NEW YORK STATE MUSEUM 



Didy mograpt US bif i du8 Elles. Quar. Jour. Geol. Soc. 1898. 54:511 

 Didymograptus bifid us EUes & Wood. Monogr. Brit. Grapt. pt 1 . Pal. Soc. 



vol. for 15)01. p.42, fig.26a and b 

 Didyiiiograptus bifidus Ruedemann. N. Y. State Paleontol. An. Rep't. 1902. 



p.566, 567 



Description. Nema and primary disk not observed. Sicula long and 

 slender, about 2 ram long. Branches dependent, rounded at their base, then 

 straight ; angle of divergence of first thecae 90° to 100°, 

 that of branches mostly varying between 20° and 25° ; 

 the branches attaining a length of 26 mm, expanding 

 gradually to a maximal width of 2.4 mm near the distal 

 growing ends, the lattei- showing a rapid contraction. 

 Thecae closely arranged, nimibering 13 to 15 in 10 mm, 

 inclined at an angle of 45° in the mature and of about 

 30° in the proximal parts ; two to three times as 

 long as wide; in contact for one half of their length 

 in the proximal and three fourths in the mature parts. 

 Apertural margin slightly concave, forming an angle of 

 135° with axis of branch. 

 Position and localities. In the Deep kill section common, but restricted 

 to graptolite beds 3 to 5, which represent the zone with P h y 1 1 o g r a p t u s 

 anna and J), bifidus. Hall records it from Point Levis and from a 

 point 3 miles above the river St Anne; Gurley lists it [1896] as a fossil of 

 the Phyllograptus anna zone (St Anne zone), and also as occurring 

 in the Upper Levis zone (zone with Diplograptus dentatus, etc.), 

 from which it is absent at the Deep kill. He i-eports it further from Nevada 

 [ibid. p.304]. According to Ami the species occurs in various localities in 

 the pi-ovince of Quebec [1889, p. 1 16k]. In Great Britain this species is, 

 according to Lapworih, EUes and Wood, '* more common than any other 

 member of the dependent series ; it occurs in great numbers at one particular 

 horizon, namely, in the Upper Arenig beds below the zone of D . m u re h i - 

 s o n i ". It is cited there from various localities in Ireland, Scotland, Eng- 



Fig. 86 Didymosrrap- 

 tus bifidus Halltf/). Por- 

 tions of rhabdosomes en- 

 larired to show the form of 

 the thecae. Deep kill. x5.25 



