INTRODUCTION. 19 



The character of the nervation remains, however, the same. It is some- 

 what obscured in the figure from indistinctness of the specimen. In figs. 

 1 and 2, representing leaves entirely preserved and nearly round, the 

 nervation is marked by three pairs of primary nerves on each side of the 

 midrib, and under them by one pair of true marginal veinlets curving on 

 each side toward the borders. Comparing, therefore, these peltate leaves 

 with fig. 4, the position of the petiole is the only notable difference, and the 

 transition to fig. 5 by slight modifications of characters is easily remarked. 

 The peltate form of these round leaves has suggested the fitness of a slight 

 modification in the characters assigned to the genus Pterospermites in the 

 "Cret. FI." (p. 94), the leaves being sometimes rounded or subcordate at 

 base. The difi"erence is immaterial, and is remarked even upon leaves of 

 the same species of Menispermum of our epoch. These round peltate 

 leaves, for example, are so much like those of living species of Oissampelos, 

 that they rather prove the adaptation of this generic division to all the 

 Cretaceous leaves which I have referred to it. 



The Magnoliacece are more numerously and definitely represented in 

 the North American Cretaceous Flora than they are in that of Europe. 

 Magnolia alternans and M. Capellini have been described by Heer in his 

 "Phillites Cretacees du Nebraska;" and since that time these two species 

 have been recognized throughout the whole explored area of the Dakota 

 Group, as also in the lower stage of the Cretaceous of New Jersey, and in 

 the Upper Cretaceous of Greenland. M. speciosa of Moletein has been dis- 

 covered in Colorado with a fruiting cone or carpite of this genus. Two 

 other species have been described from the Dakota Group: one, M. ohomia, 

 by Dr. Newberry, in his "Ancient Floras," another, M. tenuifolia, in "Cret. 

 Fl.," and two new ones, M. ohtusata and M. Ishergiana, by Heer, from 

 Atane. In Europe, M. amplifolia and M. speciosa are described by Heer 

 in the Flora of Moletin — there represented by leaves and fruit. 



To the same order belongs Liriodendron, so easily recognized by the 

 peculiar form of its leaves. Its Cretaceous origin, or rather existence, is 

 marked in the Dakota Group by a number of specific representatives locally 

 and distantly distributed. The genus is not represented in the Cretaceous 

 Flora of Europe ; but in the " Cretaceous Flora of Groenland " Heer describes 

 six varieties of Liriodendron Meekii from Atane, and no less than eight 



