GRAPTOLITES OF NEW YORK. PART 1 



691 



land (Lake district and Shropshire) and Wales. Brogger identified a form 



of the middle part of the Phyllograptus shale of the neighborhood of Christi- 



auia, with some doubt, with D. bifid us; and Herrmann cites this as a 



somewhat divergent form from Norway. In kScania (Sweden) it occurs 



in the Phyllograptus typus zone, associated with the same fauuule as in 



America. In Bohemia it is found, according to Perner, 



in D Ir, associated with a great number of other 



dependent forms. Barrois reports it as a common 



fossil in the schists with Belle roph on oehlerti 



at Boutoury near Cabrieres, in the Languedoc. The 



species has not yet, to my knowledge, been found in 



Australia, nor have the other dependent forms been 



announced from there; and it is therefore probable 



that the zones characterized by these forms have not 



yet been met with. It can be inferred from its 



general distribution that it, Avhile characteristic and 



best developed in the zone which we have named 



after it, also extends into the next higher zone in 



various regions. 



Pis'. 87 D i d y m o o- r a p 1 11 s 

 bifidus Hall sp. Shows the 

 "pustules," the common canal 

 and the thickened apertures. 

 Deep kill, x 7 



Remarhs. This Avidely distributed species is the 

 type around which group themselves the dependent species of Didymograptus, 

 most of which it precedes. It has been carefully described by several ^vriters, 

 lastly by the monographers of the British graptolites. The latter observed that 

 two groups or types of forms could be recognized by the angle of divergence, 

 that both, however, are connected by a long series of intermediate forms. We 

 have noticed only one of these groups, i. e., the one with a small angle of 

 divergence. This is also the more common form in Great Britain. 



One of our specimens [text fig. 87] in which the common canal and the 

 first theca were pyritized, shows that the latter originated about midway 

 between the apex and aperture of the sicula, grev\' a short distance along the 

 sicula and then turned to one side. The second theca appears to originate at 

 or near the geniculation of the first theca. 



