DESCRIPTIONS OP SPECIES. 13 



This elegant fern is apparently distinct from any species hitherto 

 described. In general aspect it is not unlike Pecopteris Torelli Heer (Fl. 

 Foss. Arct, Vol. I, p 88, PI. I, figs. 15a, 15b), but in that species the pinnules 

 are longer, more oblique, more acute, and the nervation more open. It also 

 has some resemblance to Cheilanthes Laharpii Heer (Fl. Tert. Helv. Vol. I, 

 p. 37, PI. X, figs. 3a, 3b). That species is, however, more delicate, the 

 pinna; more widely separated, the pinnules to a less degree imited, the 

 basilar pair similar to the higher ones, the nervation more open. 



The upper portion of the frond of this fern, where the pinnae are not 

 distinctly lobed, but simply undulate, bears a strong resemblance to that 

 figured and described in Gardner and Ettingshausen's British Eocene Flora, 

 Part II, p. 43, PI. VI and PL X, figs. 2-4, under the name of Gleichenia 

 Hantonensis (Wanklyn), but the secondary nerves are fewer and given off 

 at a more acute angle. 



The middle portion of the frond of our plant is, however, conspicu- 

 ously different, since the pinnte are deeply lobed, forming distinct and 

 peculiar pinnules at the base instead of being confluent as in G. Hantonensis. 

 It seems to be probable, however, that both ferns belong to the same genus. 



What this genus should be called must remain a matter of doubt until 

 specimens shall be obtained in which the fructification is shown. Without 

 better evidence than we yet possess, the reference of our plant to Gleichenia 

 seems to be unwarranted. 



The general form of the frond and the nervation are more like those 

 of some species of Cheilanthes than of any other living ferns with which 

 this has been compared; but it will be necessary to have the fructification 

 before the identification with that genus can be regarded as established. 

 It has been thought better, therefore, to place it in the convenient receptacle 

 afforded by the fossil genus Pecopteris, with a suggestion of its probable 

 affinities in the living flora of the world. 



The figures given represent, 5, the middle portion of the frond; 6, the 

 upper part, and 5a, the lower two pinnules at base of pinna on the under 

 side enlarged. They were collected by Dr. C. A. White, from the Green 

 River shales. 



Formation and locality: Tertiary (Green River group). Green River, 

 Wyoming. 



