GRAPTOLITES—GRAPTOLITOIDEA. 3 1 



19. D. bifidus Hall. (Fig. 47, <:, 48.) Lower Ordovicic. 



Divergence of branches 1 5° to 20 , gradually widening through 



increase in length of hydrothecae to about two thirds distance from 



Fig. 47. a (upper), Didymograptus nitidus \ b, D. Fig. 48. Didymogaptus 



patuhts ; c (lower), D. bifidus (all enlarged). bifidus. 



base, then narrowing again to apex. Shales of upper Beekman- 

 town age (Deep Kill), Point Levis and Hudson Valley. 



20. D. nitidus Hall. (Fig. 47, a, 49, a.) Lower Ordovicic. 

 Thecae closely arranged, margin slightly concave, rectangular to 



axis of theca. Branches with wide angle of divergence (nearly or 

 quite 180 ). Lower Ordovicic of Point Levis and Hudson Valley 

 (Beekmantown). 



21. D. patulus (Hall). (Fig. 47, b t 49, b.) Lower Ordovicic. 



*** "ummmmmmmmmmmm* 



*************** 



FlG. 49. a (upper), Didymograptus nitidus ; b, Didymograptus patulus. 



Differs from D. nitidus in its wider and more rapidly widening 

 branches, with ends of hydrothecae concave and strongly acute in- 

 stead of rectangular. 



Lower graptolite shales (Beekmantown) of Point Levis and 

 Hudson Valley. 



Suborder Axonophora Freeh. 



XI. Climacograptus Hall. 

 Simple rhabdosomes, with parallel hydrothecae, their outer 

 margin straight and parallel to the axis of the stem. Ordovicic. 



