ixsQL-EREux.] EEVIEW OF CEETACEOUS FLORA. 325 



Tation, and by tlieir base narrowed to the petiole, a more evident 

 affinity to species of Cissus, or Vitis, than to those of Poptdus. 



In regard to the distribution of Fopulus, to which is referred the most 

 ancient dicotyledonous leaves known as yet, that of the Lower Creta- 

 ceous of Greenland, it has, as said above, three species known already in 

 the Upper Cretaceous of that same country, and five or six in the 

 Dakota group. It has, however, not been remarked in any Cretaceous 

 flora of Europe. It is not mentioned in the review of the genera repre- 

 sented by the, as yet, undescribed species of Aix la Chapelle, and no 

 form even distantly related is described in the Lower Paleocene flora of 

 Gelinden. It has, however, one species in the Eocene flora of Sezane, 

 and increases in the number of its representatives in all the stages of 

 the Miocene. As far as we know it, till now, it has few species in our 

 Lower or first American Tertiary group, the Eocene; a large propor- 

 tion, eight per cent, of the species, in the second ; still more, or twelve 

 per cent., in the third 5 and is scarcely present in the fourth, the Green 

 River gToup. 



The presence of willows, species of Salix, in the flora of the 

 Dakota group is not controverted; the reference of leaves by which 

 the genus is represented in this formation is evident. As it is seeti 

 in Cretaceous Flora, p. 60, PI. V, figs. 1-4, I have described as refer- 

 able to one species only, a number of leaves somewhat different in their 

 size and their shape. As the specimens representing them are from the 

 same locality, and as I recognized upon some of them fragments of leaves 

 with all differences of size, forms, and even consistence and color, 

 I considered them as mere variations of leaves of a same tree. Dr. 

 jSTewberry has from the same formation four species which, he says, he 

 has chosen to regard as distinct, for geological convenience. No salix 

 has been recognized as yet in any stage of the Cretaceous of Green- 

 land ; but one species, Salix Hartigii, Denk, is from the quader sand- 

 stein of Germany, and another, Salix Goetziana, Heer, from Quedlin- 

 burg. The genus is therefore sparingly represented in Europe and 

 i«rorth America in Cretaceous floras which are considered as nearly 

 synchronous. The other genera of the Ameutacese, Betula, Alnus or 

 Alnites, Myrica, Quercus, Fagus and Ficus, to which leaves have been 

 referred in the Cretaceous Flora, do not require any observations. In 

 this case, as in all the determinations of fossil plants, the characters of 

 the species are not always satisfactorily established, but the generic 

 affinities have been recognized or passed without any marked criticism. 

 The generic relation is especially positive for the remains referable to 

 Myrica, which was already represented in the Cretaceous Fiora by one 

 fragmentary leaf and by seeds, and to which a fine new species is added 

 in this memoir. It seems equally so for Quercus or its peculiar division, 

 Dryophyllum, of which we have two new species, and for Ficus, to which 

 one species is added. 



Specimens of leaves referable to Platanus have been found in moder- 

 ate proportion both in Nebraska and Kansas. The first was described by 

 Heer, in the " Phyllites du Nebraska," as Platanus Newberryi, from a very 

 incomplete fragment. The accuracy of this determination was, however, 

 subsequently testified by the discovery of more complete leaves figured 

 in Cretaceous Flora, PI. VIII, figs. 2 and 3, and PI. IX, fig. 3, which show 

 the narrowed base descending along the petiole lower than the point 

 of union of lateral j)rimary veins, and also the tendency to a three-lobed 

 division, characters which were not observable in the fragment which 

 Professor Heer had for his examination. To this fine species have 

 been added: Platanus primceva, de&chhed from leaves so remarkably 



