40 THE LATER EXTINCT FLOEAS OF NORTH AMERICA. 



species that I am compelled to regard them as distinct till proof is furnished 

 to the contrary. 



Formation and locality: Tertiary (Eocene?). Banks of Yellowstone 

 River, Montana. 



Populus (?) cordifolia Newb. 



PI. Ill, fig. 7 ; V, fig. 5. 



Ann. N.Y. Lye. Nat. Hist.,Vol. IX (April, 1868), p. 18; Ills. Cret. and Tert. PI. (1878), 

 PI. V, fig. 5. 



"Leaves heart-shaped, slightly . decurrent on the petiole ; margins entire; 

 nerves fine but distinctly defined; medial nerve straight or slightly curved, 

 running to the margin ; lateral nerves, six on each side, given off at an angle 

 of about 50 degrees, nearly parallel among themselves, straight near the 

 base of the leaf, slightly curved toward the summit; lower lateral nerves 

 giving off on the lower side about four simple or once-forked, slightly 

 curved branches, which terminate in the basilar margin; second pair of 

 lateral nerves giving off about three similar branches on the lower side, 

 which run to the lateral margins; third pair supporting about two, and 

 fourth pair one branch on the lower side near the summit; tertiary nerves 

 springing from the secondary nearly at right angles, slightly arched and 

 running across nearly parallel to connect the adjacent secondary nerves." 



Collected by Dr. F. V. Hayden. 



In its general aspect this species closely resembles the preceding-, but 

 several specimens which I have before me agree in being less rounded and 

 more heart-shaped, and the lateral nerves are more numerous and given off 

 at a larger angle. 



In these leaves the basilar nerves reach the lateral margins below the 

 middle, and their second branches, as a consequence, have more the aspect 

 of some of the leaves of the Cupuliferse, such as Corylus. The latticelike 

 arrangement of the tertiary veins in this, as in the other species of the 

 group, is very characteristic of the Cupuliferse, though not strictly limited 

 to them. If we could imagine a Corylus with rounded or broadly cordate 

 leaves, of which the margins were entire, we should have a very near 

 approach to these plants. 



Formation and locality: Cretaceous (Dakota group). Blackbird Hill, 

 Nebraska. 



