42 THE LATER EXTINCT FLORAS OF NORTH AMERICA. 



precisely similar one is figured by Lesquereux on PL IV of his Cretaceous 

 Flora. It is more than doubtful whether any of these leaves belong to a 

 true Populus; the nervation is more distinctly and regularly pinnate than 

 in any living species of the genus, and the probability is that we have here 

 the relics of a genus of trees now extinct, but closely related to the poplars. 

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

 Nebraska, and Fort Harker, Kansas. 



Populus (?) Debeyana Heer. 



PI. IV, fig. 3; V, fig. 7. 



Nouv. Mem. Soc. Helv. Sci. Nat., Vol. XXII (1866), p. 14; PI. I, fig. 1. 



Juglans Debeyana (Populus?) Heer, Lesq. Am. Journ. Sci., Vol. XLVI (July, 1868), 



p. 101. 

 Juglans (?) Debeyana Heer, Lesq. Cret. Fl. (1874), p. 110, PI. XXIII, figs. 1-5; Ills. 



Cret. and Tert. PI. (1878), PI. IV, fig. 3; V, fig. 7. 



A number of leaves in the collection made by Dr. Hayden are clearly 

 identical with that referred with doubt by Professor Heer to Populus from 

 the generalities of its nervation, and impressions of what would seem to have 

 been glands at the base on either side of the point of insertion of the 

 petiole. In our specimens, however, there are no glandular impressions, 

 and the departure from the normal type of nervation in Populus noticed 

 by Professor Heer is still more conspicuous. 



The strong pair of basilar nerves so characteristic of the poplars is 

 entirely wanting, the inferior lateral nerves being small, and the stronger 

 ones, which succeed them above, are not opposite. In view of the marked 

 departure which these leaves exhibit from the nervation and form of the 

 typical poplars, Professor Heer suggests that they may represent an extinct 

 genus of the order Salicineaa, but it seems to me their affinities are closer 

 with the Magnoliacese, and that it is even probable that they represent a 

 species of the genus Magnolia. 



Lesquereux has suggested that this leaf should be referred to 

 Juglans, comparing it with J. latifolia Heer, from the Tertiary of Switzer- 

 land; but a considerable number of specimens before me fail to convince 

 me of the justice of this reference, and yet they hardly suggest any other 

 botanical relations. The leaves were evidently very thick and leathery, 

 and the nervation is crowded and strong. It will be necessary that some 



