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whose essential characters are recognized in the species of this country 

 M. canadense is now the consort of our Platawus, Magnolia, Tulip-tree, &c. 

 It grows under the same climatic circumstances, and has the same habitat. 

 As the leaves of the Dakota group, compared to this species, are like it — 

 peltate, round or cordate, obtusely angular, of the same nervation and consist- 

 ence — there is reason, indeed, to refer it to this genus rather than to any other 

 having no representatives among us. 



No species of Menispermum or Menispermites has been recognized from 

 the geological formations, except the species of the Dakota group. One leaf, 

 however, is described by Unger as Acer obtusilobum, which appears to me a 

 true Menispermites. It has the secondary nervation of Menispermum, (Coc- 

 culus) carolinum, and the basilar veins come out from the borders of a round, 

 notched base, as in a peltate leaf. Unger doubtfully considered this leaf as a 

 species of Acer. Till now, we have not seen any appearance of organs of this 

 last genus, either leaves or seeds, in the Dakota group, as we have none also 

 in the Eocene. The maple seems to be of more recent origin, as it is remarked 

 hereafter. However, one Cretaceous leaf, or the fragments of a double leaf 

 are referred with doubt to the genus Negundo. As the leaf is not complete, 

 its outline indefinite, it is useless to argue upon its possible affinity ; and for 

 this, as for some others, we have to wait for the discovery of more perfect 

 materials. 



The i-elation of other leaves of the Dakota group to the genera Paliurus 

 Rhamnus, Juglans or Rhus, and even Prunus, appears sustained by sufficient 

 evidence. The characters of the leaves of Paliurus and Rhamnus are not 

 likely to be mistaken. Both these genera have identifiable remains in the Ter- 

 tiary of the Rocky Mountains ; one Paliurus is found in the Eocene of Golden 

 and Black Butte, and another in the Miocene of Carbon and Washakie. This 

 last is an arctic species, also recognized by Heer in the Miocene of Green- 

 land and Spitzbergen. Rhamnus is especially well represented in our Lower 

 Tertiary. Eight species are described from Golden, Black Butte, and the 

 Raton Mountains, four of which are in the Miocene of Europe, where the 

 genus has fourteen species. It is, therefore, an old type, well established at 

 the beginning of our Tertiary period j 1 and it is not surprising to find it already 

 in the Upper Cretaceous flora. Its present distribution is mixed. The genus 

 preserves its predominance in Europe by the number of its species ; it has 

 there more than a dozen, while in North America it has only four or five. 



1 The leaf described under the name of Rhamnus tenax, is considered by Count Saporta as a Salix. 



