2 4 



XORTH AMERICAX INDEX FOSSILS. 



3. Branches leaf-like, four rows of hydrotheca?, generally appearing as two 



rows from compression IX. Phyllograptus. 



AxONOrHORA. Virgula present 4. 



4. Branches with a single row of hydrothecae or only partly with double row cc. 



cc. Branches entirely distinct, only a single row of hydrothecae (Mon- 

 oprionidian) opening in a direction opposite to the sicula. 



X V . Man og rap tits . 



cc. Two branches, more or less united m. 



m. Branches united only at base, V-shaped with hydrothecae gen- 

 erally on outside XIII. Dicellograptus. 



m. Branches united for some distance, above the base, Y-shaped. 



XII. Dicranograptus. 

 4. Branches with double row of hydrothecse throughout (Diprionidian).. dd. 



dd. Periderm solid n. 



}i. Hydrotheca? sharp XIV. Diplograptus. 



n. Hydrotheca; blunt XI. Climacograptus. 



dd. Periderm a fine mesh work XVI. Retiolites. 



SYNOPSIS OF GENERA AND SPECIES. 



Order I. DENDROIDEA Nicholson. 



I. DlCTYONEMA Hall. 



Rhabdosomes forming funnel or fan-shaped fronds, composed of 

 numerous bifurcating branches arising from an acute base, and 



united at intervals by thin cross bars 

 or dissepiments. Hydrothecse sel- 

 dom well preserved, of several types, 

 appearing occasionally as teeth or as 

 pits on the side of the branches 

 turned toward inside of the funnel. 

 Camb.-Dev. 



1. D. flabelliforme (Eichwald). (Fig. 

 32.) Upper Cambric. 

 Rapidly expanding cones up to 

 ten or twelve inches in length. 

 Branches about .4 mm. wide, sub- 

 parallel, rigid, bifurcating at long in- 

 tervals, separated by a little over I 

 mm. Dissepiments about half as 

 thick as the branches. 

 In the shales forming the uppermost Cambric beds of eastern 

 North America (especially in eastern Canada) and widely distrib- 

 uted in Europe. 



Fig. 32. Dictyonema flabelliforme 

 (after Matthew). 



