DESCRIPTION OF SPECIES— FILICES. 49 



FILICES. 



The Ferns are, after the Li/cojjodiacece, the oldest vegetables of the world. 

 From the Devonian, where already a number of species of peculiar types are 

 known, they become more and more numerous and predominant up to tlic 

 end of the Carboniferous; for, in this formation, they compose at least one- 

 half of the vegetation. After this, in the Permian, the Trias, the Jurassic, 

 and the Cretaceous, they are subordinate in number to the other groups of 

 plants, represented, however, in constantly modified characters appropriate 

 and particular to the different epochs. The Gkichenia, for example, appear 

 in the Jurassic, become predominant through the whole Cretaceous formation, 

 wherein a comparatively large number of species has been observed in the 

 Arctic zone, in Europe, and also in the Dakota group of Nebraska. In tlie 

 Tertiary, they disappear most entirely, and therefore it is not at all surprising 

 that among the numerous species of Ferns described from the Lignitic there 

 is no Gleickenia. This absence of a genus truly Cretaceous and generally 

 distributed through this formation, present also in the Dakota group, is, 

 among others, an important point of evidence of the Tertiary age of the 

 Lower Lignitic flora. 



SPHENOPTERIS, Brgt. 



Sphcnopicris L.akcsii, Lesqz. 



Plate II, Figs. 1-1 a. 



S^henopteris Eocenica, Eti., Eoc. Fl. d. M. Prom., p. 9, pi. ii, figs. 5-8.— Lesqx., Annual Report, 1872, p. 376. 



Frond large, at least tripinnately divided ; secondary pinnaj long, linear-lanceolate, oblique to a 



balf-round, n.arrow racbis ; piuunles obliquely turned upward, close, contiguous, and united below tbo 



middle, acutely lobed; veins pinnate; divisions simple or forking once. 



As remarked in the first description of this species, it differs evidently 

 from the one described under this last name by d'Etlingshausen {loc. cit.) by 

 the connection of the pinnules from below the middle, while they are separated 

 from the base in the European species; by the sharply pointed lobes of the 

 pinnules, described and figured as obtuse by the author, and also by the 

 nervation. In this species, the secondary veins are strong, flat, generally 

 simple, each of the divisions ascending to the point of a lobe. These differ- 

 ences are marked enough to force the separation of this species. From the 

 fragments seen of this fine Fern, it has the same characters in all the subdi- 

 visions of its fronds; at least the secondary pinnae are sessile, connected at 



4 T p 



