VI AUTHORS PBEFACE. 



because the list does not profess to be critical, but takes the 

 name and the horizon given by the original describer of each 

 species. Therefore, the names of a number of the horizons 

 will be recognisably out of date ; but I thought it useful to 

 have the original descriptions catalogued for reference. Further, 

 a number of plants from the Laramie have been included in the 

 list, because in many cases they were described as Cretaceous, 

 though they may be well known to-day to belong to the 

 Tertiary. I included most of those species which had been 

 much quoted as Cretaceous, because it appeared to me that for 

 a reader not intimately acquainted with the Cretaceous, it would 

 bo useful to have a list in which references to the original 

 descriptions could readily be found. 



Lastly, a point whicli may make the list appear very in- 

 complete, must be mentioned. Many of the species originally 

 described under one genus have been removed from genus to 

 genus at the hands of various writers. If all the species had 

 been entered under all the geaeric names ever given to them, 

 the list would have been even bulkier than it is at present. 

 Consequently, while I endeavoured to enter in my list any 

 re-naming that was enlightening, or accompanied by any original 

 work on the specimen, I deliberately left out many of the cases 

 (which are so numerous relating to badly preserved leaf-impres- 

 sions) in which a species had been transferred to various genera 

 on the grounds of nomenolatorial rules or the personal prefer- 

 ences of an author who neither re-figured nor re-described the 

 specimen, nor in any way added to our knowledge of it. Never- 

 theless, a good many cross-references to the different genera 

 under which a species appears, will be found. As an example 

 of the type of name which I have tended (perhaps arbitrarily) 

 to omit, Dryojriteris virginica may be mentioned. Under As- 

 pidium Fontaine described a considerable number of species 

 A. virginicum among them. In Knowlton's list of Cretaceous 

 plants, 1898, he transfers most of these to the genus Di-yoptens, 

 his entry regarding them being in this form : " Dryopteris vir- 

 ffiniea (Font.) n. comb.," followed by reference to Fontaine's 



