GEOLOGICAL HISTORY OF THE WALNUTS 235 



existing genera are monotypic, it is quite safe to predict an inter- 

 esting and extending geological history. Engelhardtia proves 

 to be another illustration of this principle, for its peculiar three- 

 winged fruits have been known in the fossil state for almost a 

 century. They were long unrecognized, however, and the earlier 

 students who described them compared them with the somewhat 

 similar winged fruits of the genus Carpinus (Betulaceae). With 

 the botanical exploration of distant lands in the early part of the 

 19th century, specimens of Engelhardtia began to be represented 

 in the larger European herbaria, and Baron Ettingshausen, that 

 most sagacious of paleobotanists, as long ago as 1851 pointed 

 out that certain supposed species of Carpinus were really fruits 

 of Engelhardtia. He returned to the subject in 1858 without, 

 however, actually changing the names of any of the supposed 

 species of Carpinus nor does he seem to have been aware of the 

 existence of a living species of Engelhardtia (Oreomunnea) in 

 Central America. 



Since Ettingshausen's announcement a dozen or more fossil 

 species have been described. The oldest known European form 

 occurs in the upper Eocene or lower Oligocene (Ligurien) of 

 France and the species become increasingly abundant through- 

 out southern Europe especially toward the close of the Oligocene 

 and the dawn of the Miocene, Saporta stating that the slabs 

 from the leaf-beds at Armissan in southeastern France are thickly 

 strewn with their peculiar fruits. Fossil forms continue in Europe 

 throughout the Miocene and Pliocene and specimens of late 

 Miocene or early Pliocene age are recorded from Spain, France, 

 Italy, Croatia, and Hungary. 



The only described species from America occurs somewhat 

 earlier than any of the European forms, being found in the Lower 

 Eocene (Wilcox Group) of northern Mississippi. The type figure 

 of this form is reproduced in figure 3. This is not the only known 

 species from America, however, as fossil leaves of this or other 

 species occur at the same horizon and an additional species with 

 smaller fruits has recently been discovered by the writer in the 

 Middle Eocene (Claiborne Group) of southern Arkansas. 



