I70 THE RARITAN FLORA. 



actly the same texture and venation, the same variabihty in out- 

 line and marginal undulations, the same stout midrib and con- 

 spicuously alate petioles. In examining a suite of specimens of 

 the latter and comparing them with the fossils the conclusion 

 seems to be irresistible that they are related, and the writer has 

 consequently referred the fossils to a new genus which empha- 

 sizes this relationship to the modern genus. Ail of the fossil 

 specimens which are at all complete are figured on Plate xxi, 

 and two modern leaves are introduced for comparison. Possible 

 arguments against the pnesent view may be based on the theory 

 that the modern alate petioles are derived from ancestors with 

 compound leaves ; in fact, some modern species still have tri- 

 foliate leaves, and if this were true of the fossils as well, it would 

 require considerable rapidity of evolution in this genus previous 

 to the mid-Cretaceous. The modern leaves absciss from the top 

 of the petiole, and would be unlikely to occur as fossils with the 

 petiole attached, neither can any indication of such an abscission 

 line be made out in the fossils. This is the most difficult argu- 

 ment to combat. However, modern leaves are sometimes shed 

 in their entirety, and we are justified in predicating the occasional 

 fall of leaves before maturity when the abscission layer of cells 

 had not yet become weakened. The agency might be violent 

 winds, the passage of large animals like some of the Cretaceous 

 dinosaurs, or weakened conditions due to insect or fungous dis- 

 eases. 



Occurrence. — South Aniboy. 



Collections. — U. S. National Museum. 



