(69) 



Poi'ULiTKs Lesq. Am. Jour. Sci. 46: 93. 1868. 



Founded by Lesquereiix to include leaves from the Dakota 

 Group which are apparently related to Populus but differing 

 in their generally entire margin, cordate outline, and cras- 

 pedodrome venation, the latter character apparently wanting 

 in our species. Some of Lesquereux's species have since been 

 transferred to the genera Grezut'ofsis, Hamamclites, Mcnis- 

 pennites, and C/ssitcs, leaving seven Dakota species and one 

 species from the Upper Cretaceous of Vancouver Island. 



The genus Populus, although containing the oldest known 

 dicotyledon at Kome, besides ten Dakota species and two 

 Potomac species according to Fontaine, is so essentially a later 

 genus that I prefer to include our leaf in the related genus 

 Populites, thus obviating too great definiteness of relation to 

 the existing genus. 



Populus contains about twenty-five species in the existing 

 flora, all of which are confined to the northern hemisphere. 

 Some twelve of these inhabit North America. The fossil 

 species are numerous. 



Populites tenuifolius sp. nov. PL ^g. f. 7. 



A leaf exceeding 10 cm. in length and nearly 12 cm. in 

 width : margin in the upper part apparently entire or perhaps 

 a trifle undulate ; about 4 cm. of the right lateral margin is 

 preserved and seems to be slightly crenate, but the indica- 

 tions are very faint and may be due to the wearing away of 

 the material. The base is not preserved, but I judge it to 

 have been cordate. The texture is extremely thin for so 

 large a leaf. Secondaries four or five on each side, very 

 thin, alternate, unbranched except the basal ones, leaving 

 the midrib at an angle of about 45^ and curving upward, 

 branching near the margin much as in ProtophyUum Stern- 

 bergii;* basal secondaries evidently much longer than the 

 others, giving off numerous branches to the latero-basal 

 portion of the leaf. Areolation ill-defined, angular. 



I have been at a loss to correctly determine this leaf ; it 

 bears considerable resemblance to some of Lesquereux's 

 species of Pretophylluni, but inasmuch as the latter is a syn- 



* Lesq. Fl. Dak. Group, pi. 42. f. /. 



