8 CEETACEOUS AND TERTIARY FLORA. 



P. cyclophylla, described in Proc. Acad. Nat. Sci., Philadelphia. Professor 

 Newberry, in his paper "On the Later Extinct Floras of North America," 

 has described, also, besides the doubtful P. (?) Beheyana, three new species : 

 Populns (?) cordifolia, P. elliptica, and P. microphylla. The specification 

 and the interrogative punctuation applied to some of these names show 

 that the authors themselves do not consider the generic reference as defin- 

 itive, the character of some of the leaves being somewhat in disagreement 

 with those generally recognized in species of Populus of our present time. 

 Indeed, species of this kind, like the present P. alba, for example, have 

 such multiplied and diversified forms of leaves, such great variability in 

 their nervation, the mode of attachment, the length of the petiole, etc., that 

 they readily offer, by comparison with fossil leaves of obscure relationship, 

 some points of affinity which, not being found elsewhere, have to be con- 

 sidered by the authors. Hence the doubtful references which may be, 

 and are often, rectified by subsequent discoveries, as is proved by the great 

 proportion of synonyms appended to the enumeration of Populus species. 

 To obviate this inconvenient multiplication of fluctuating species of Pop- 

 ulus I proposed a new generic division, under the name of Populites, for 

 the classification of those Cretaceous leaves, numerous indeed, which, 

 partaking of some of the characters of Populus, are nevertheless removed 

 from this division by some others, as remarked in the first memoir which 

 I published on some Cretaceous plants from Nebraska. 



This paper had to be prepared on short notice from a limited number 

 of specimens, but since its publication I have had opportunity to study 

 the specific forms of the Cretaceous Flora by comparing a very large num- 

 ber of specimens, and have thus been able to recognize a more evident 

 affinity of some of those leaves referred to Populites with other generic 

 divisions. Populifes Lancastriensis, P. elegans, Avhich Schimper admits as 

 a true Populus, and Populites cyclophyllus are the only species preserved in 

 this genus. P. ovatus, considered as possibly referable to Celtis in Creta- 

 ceous Flora, being rather related by its characters to the Ampelidece, is 

 described under the new generic division of Avipelophyllum. The affinity 

 of /'. quadrangularis being more evident with Alnus, has been described 

 as Alnites. P. flahellata, as seen from other specimens, appears to be a 

 deformed leaf of Crreviopsis Haydenii, and P. Salvshuricefolia, being related to 

 Cissus, is described as Oissites. 



