43 



but as a duty, to modify names and descriptions of fossil species which I may 

 have published formerly, whenever this change is demanded either by the 

 discovery of more perfect specimens, which may show under another light 

 the relations of a plant, or by the recognition of different characters which 

 were not observed in a preliminary examination. The first specimens fur- 

 nished me were comparatively few, mostly incomplete, and I was requested 

 to make an examination of them and to describe them, at least in a precur- 

 sory way, in a very short time. They were the materials from which was 

 written and published in the American Journal of Science and Arts, vol. xlvi, 

 July, 1868, the paper on some Cretaceous fossil plants from Nebraska. Since 

 that time I have not only received a large number of specimens from the 

 Dakota group, but at two different times I have been over the field for 

 the purpose of studying the distribution of the fossil plants, their relation to 

 localities, &c, and have had opportunities of collecting a number of specimens 

 in a better state of preservation, and, what is still more advantageous for the 

 exactitude of the determination of fossil plants, to compare in place different 

 forms related to the same species. Of course these prolonged studies and 

 the increasing amount of materials may already account for, and render ex- 

 cusable, some difference in the specifications and the synonymy remarked in 

 the following descriptions. 



Moreover, at the time when the first descriptions of these fossil plants 

 were made, there was nothing as yet known of the dicotyledonous leaves of 

 the Cretaceous, either of Europe or America, except the little which had 

 been published in the Paleontographica, by Stiehler, Zenker, and Dunker, 

 and in the Phyllites cretacees du Nebraska by Heer. As remarked by this 

 author, Debey, who has a large collection of leaves of the Cretaceous of Aix-la- 

 Chapelle in Belgium, had admitted that our fossil leaves of the Dakota group 

 had no relation whatever with those of Belgium, and that therefore no com- 

 parison could be made between them. Since that time, Professor Etting- 

 hausen has published, on the Cretaceous flora of Niedershcena of Saxony, 

 what he calls a Contribution to the acquaintance of the oldest dicotyledonous plants 

 of our earth, and Heer, also, has given on the Cretaceous flora of Moletin, in 

 Moravia, and on that of Quedlinburg, two very fine quarto memoirs, affording, 

 like that of Ettinghausen, a few points of comparison for the present study 

 of the flora of the Dakota group. Notwithstanding this supplement of male- 



