GRAPTOLITES. 23 



1892. Gurley, R. R. The Geologic Age of the Graptoiite Shales of 

 Arkansas. Ark. Geol. Surv. Ann. Rep., 1890, 3: p. 401. 



1895. Matthew, G. F. Two New Cambrian Graptolites with Notes 

 on Other Species of Graptolitidae of That Age. N. Y. Acad. Sci. 

 Trans., Aug., 1895. 



1896. Gurley, R. R. North American Graptolites. Jour. Geol., 

 Vol. 4, no. 1, p. 63 ; no. 3, p. 291. 



1904. Ruedemann, R. Graptolites of New York. Part 1. N. Y. 

 State Museum Memoir, 7. 



[This is the most comprehensive and most important work that has 

 appeared in this country since Hall's Graptolites of the Quebec Group.] 



Key to the Genera. 



I. DENDROIDEA. Rhabdosomes irregularly branching in a shrub-like funnel or fan- 



like manner. Hydrothecae mostly in the form of pits, rarely prominent.. A. 



A. Branches joined at frequent intervals I. 



I. Branches joined by cross-bars or dissepiments I. Dictyonema. 



1. Branches flexuous, coalescing at points of contact ; dissepiments rare. 



II. Desmograptus. 



A. Branches not joined, or only at great intervals 2. 



2. Branches diverging aa. 



aa. Branches stout, bifurcating, irregularly dendroid. 



III. Dendrograptus. 

 aa. Branches plumose, with branchlets arranged alternately on oppo- 

 site sides IV. Ptilograptus. 



2. Branches parallel, bifurcating at intervals Callograptus. 



II. GRAPTOLOIDEA. Rhabdosomes simple or branching but not shrub-like. 



Hydrothecae commonly distinctly marked B. 



B. Axonolipa. Virgula absent 3. 



3. Branches with single row of hydrothecae (monoprionidian) bb. 



bb. Branches of rhabdosomes bifurcating at irregular intervals, nu- 

 merous k. 



k. Branches apparently four at center, making a cross. 



V. Staurograptus. 



k. Branches two at center x. 



x. Primary branches S-shaped VI. Cainograptus. 



x. Primary branches not S-shaped Bryograptus. 



bb. Branches of rhabdosome regularly bifurcating /. 



/. Branches more than 8 y. 



y. Three bifurcations (sometimes more) producing 16 branches. 



VII. L oga n ograptus . 

 y. Numerous bifurcations, regularly alternating. 



VII. Goniograptus. 



I. Branches 8 or less z. 



z. Branches 8, sometimes 6 VII. Dichograptus. 



2. Branches 4 VIII. Telragraptus. 



z. Branches 2 X. Didymograptus. 



