34 



Order Terebinthince. 



Juglans, L 1 



Rhus, L , 1 



Order Calophytcc. 



Py rus, Lindl 1 



Prunus, L .' 1 



Order Leguminosce. 

 Leguminosites, Heer 1 



Incertez sedis. 



Eremophyllum, Lsqx 1 



Phyllites, Auct 5 



Ptenostrobus, Lsqx 1 



Caulinites, Heer 1 



Carpolitb.es, Sternb 2 



The table indicates one hundred and thirty species, distributed according 

 to descriptions in seventy -two genera, or about two species to each genus. 

 From this it would seem right to suppose, for the determination of the Creta- 

 ceous fossil leaves, a certain degree of reliable positiveness which could not 

 be expected of a flora with more numerous specific divisions. For, of course, 

 the species of the geological times were more numerous, perhaps, than 

 those of our own epoch, generally more contiguous, more or less illimit- 

 able ; subject, therefore, to personal criticism or opinions. The descriptions 

 of the species of the Dakota group force a contrary conclusion. If some of 

 the genera are clearly characterized and their relation positively ascertained, 

 some others may be considered as groups of analogous forms, which point 

 to the derivation of different types, and which therefore cannot be considered 

 as homogenous or identical, though it may be difficult to divide them and to 

 limit the divisions by positive characters. Moreover, a number of those 

 ancient leaves are not referable to any of the types of our present vegeta- 

 tion. They represent apparently extinct vegetable groups, or their typi- 

 cal characters have been modified in such a way that by successive devia- 

 tions from the primitive forms the relation of the offsprings cannot be recog- 

 nized. This necessitates the admission of peculiar names in the description 

 of these groups of leaves, (Populites, Menisper mites, Phyllites, &c.,) whose af- 

 finity is merely supposed. The relation may be recognized hereafter, either 



