52 THE LATER EXTINCT FLORAS OF NORTH AMERICA. 



When the leaf is more than usually elongated, as in fig. 3, the basilar 

 nerves spring from the midrib a little below the junction of the main lateral 

 branches. The normal form is well represented in fig. 1, but it is not unu- 

 sual to see those which are slightly flabelliform, like fig. 4. The tissue of 

 the leaf would seem to have been thick and leathery, since the surfaces are 

 unusually smooth, and the nerves sunk in the parenchyma are often scarcely 

 perceptible. 



The leaves desCTibed above present some anomalies in form and struc- 

 ture as compared with most of our poplars, since they are frequently fla- 

 belliform, and were apparently of much thicker and denser tissue than 

 those of any living species. They present, however, a marked resemblance 

 to those described and figured in this report under the names of P. elliptica 

 and P. flabellwn, one from the Dakota group of Kansas, the other from the 

 Upper Cretaceous of Orcas Island on the northwest coast, and P. cuneata 

 from the Tongue River Tertiary; and all the group, in form, nervation, and 

 serration, have sufficient likeness to some of the living poplars, particularly 

 to P. tremuloides of America and P. pruinosa of Songaria, to warrant their 

 being included in the same genus. 



There are some tropical trees of which the leaves present considerable 

 resemblance to our fossils, especially one of the Proteacese {Adenantlws cune- 

 atus of Australia), the leaves of which are small, cuneate at base, rounded 

 at summit, where they are coarsely crenate, having almost precisely the 

 form of one of the specimens of the fossil in question. This is, however, 

 apparently an abnormal form, and the similarity which I have noticed is 

 perhaps accidental and certainly of little value. The nervation of these 

 fossil leaves is considerably different from that of Adenanthos, and a mere 

 resemblance in form, however close, would hardly warrant us in supposing 

 that the fossil plant could have any very near affinity with one so far 

 removed geographically and botanically from the flora with which it is 

 associated. 



Probably all the specimens represented by figs. 1, 2, 3, and 4 belong 

 to one species, though that from which fig. 3 was taken was obtained in a 

 different locality from any of the others and has a somewhat different aspect. 

 Taken by itself this might readily be supposed to belong to a rosaceous 

 plant, perhaps a Rubus, Pyrus, or Crataegus; but it would be difficult to find 

 its exact counterpart in any living species of these genera. It is perhaps 



