146 NATHORSTIA. 



probable that Schenk's specimen may be identical with the Sussex 

 examples referred to Nathorstia. It not infrequently happens that 

 the same specific and generic names have been used for Palaeozoic 

 and Mesozoic ferns, which have no resemblance to one another ; 

 and this confusion no doubt arises from the choice of terms for 

 new species from one geological horizon, without sufficiently 

 considering the names already in use for plants of a different 

 age. An instance of this is afforded by Pecopteris Geiniteii, 

 Dunk.; this name was instituted by Dunker 1 in 1846 for some 

 specimens of Wealden fern fronds from Northern Germany; in 

 1849 Gutbier 2 makes use of the same name, apparently without 

 knowledge of its previous existence, for some Permian specimens 

 from Saxony. Gutbier's species is retained in Sterzel's recent 

 Monograph on " Die Flora des Rothliegenden im plauenschen 

 Grunde bei Dresden," 3 but, in view of the priority of Dunker's 

 application of the specific name, some new term should be sub- 

 stituted in the case of Gutbier's Permian plant. Schimper 4 

 includes Gutbier's species under Pecopteris (Cyath.) pinnatifida 

 (Gutb.), Gein. Some of the pinnules in the pinnae figured by 

 Schenk appear to show venation, but there is not sufficient 

 evidence in favour of the identity of his specimen with those 

 from the English Wealden to warrant our acceptance of the 

 venation characters as characteristic of Nathorstia valdemis. If 

 specimens are found which are clearly of the same species as those 

 represented in PL VII. Fig. 5 and PI. IX. Fig. 2, and show distinct 

 venation of a type characteristic of some existing provisional genus, 

 then the name Nathorstia must be abandoned. 



There is a certain resemblance between the present species and 

 Alethopteris cycadina, Schenk, as figured in pi. xxvi. fig. 6, 

 Palaeontographica, vol. xxiii; but the agreement is very slight, 

 and the earlier figure of the same species by Schenk 5 represents an 

 entirely different plant to Nathorstia valdensis. 



1 "Wealdenbildung, p. 6. 



2 Die Verstein. Roth. Sachsen. 1849, p. 16, pi. ii. fig. 10 ; pi. ix. figs. 1-3 ; 

 pi. xi. figs. 5-6. 



3 Abh. math.-phys. Cl. k. Sachs. Ges. Wiss. vol. xix. 1893. 

 * Trait, pal. veg. vol. i. p. 507. 



5 Palaeontographica, vol. xix. pi. xxxi. fig. 2. 



