FLORA OF LAKOTA OF BLACK HILLS. 321 



Jurassic flora, it is to be expected that it would survive with modifications in the 

 Lower Cretaceous. As the description of the Oregon Jurassic plants is unpublished, 

 of course Mr. Wieland did not have an opportunity to compare the two. * * * 



Among foreign specimens presenting analogies, that figured by 

 Seward as Tmiiopteris Beyrichii (Schenk) Sew.," from the Wealden of 

 Ecclesbourne, bears quite as strong a resemblance to the Black Hills 

 specimens as any form known to me. It is broader, and the veins are 

 not so closely set. I suspect that this plant is a Nilsonia. 



Also, in his memoir on La Flore Wealdienne de Bernissart,'' Mr. 

 Seward figures bases of fronds which agree in size and form with our 

 specimens. Unfortunately, their venation is lacking. Seward compares 

 this form with Treniopteris (Oleandridium) Beyrichii (Schenk) Sew/ 

 This species is smaller and its veins sometimes fork, but the general 

 resemblance to N. nigracoUensis is marked. From Schenk's figures I 

 should say that the insertion of the lamina is intermediate between the 

 condition seen in characteristic Nilsonias where the laminae extend to 

 the center of the upper surface of the midrib and forms like Tmiiopteris 

 vittata Brongn., where the lamimie are inserted well down on the sides of 

 the prominent midrib. 



Lastly, I may mention Nilsonia polymorpha Schenk, so well and 

 fully illustrated by Nathorst in four plates, comprising many figures of 

 the beautifully preserved specimens from the Rhetic of Palsjo, Sweden."* 

 The smaller forms of these with whole margins bear a close resemblance 

 to the Black Hill fronds, and we can not doubt their generic relationship. 



As regards the generic distinction between Nilsonia and Tseniopteris, 

 after again examining all the evidence now available to me, I agree with 

 Professor Fontaine's view. It is to be borne in mind that the genera 

 Nilsonia, Tgeniopteris, and Oleandridium have now come to comprise 

 numerous species of a very generalized and cosmopolitan t^-pe of leaf. 

 As a consequence, it has become difficult, as always in such a case, to 

 say definitely, in the absence of extended revision, whei^e the one genus 



« Fossil Plants of the Wealden, Pt. I, p. 127, pi. ix, figs. 3, 3a. 

 6 M^m. Mus. Roy. d. Hist. Nat., Vol. I, Bruxelles, 1900. 

 c Palaeontographica, Vol. XIX, p. 221, pi. xxix, figs. 6, 7. 



<< Nathorst, Bidrag till Sveriges Foss. Fl. : Kongl. Sv. Vet.-Akad., Handlingar, Vol. XIV, No. 3, Stockholm, 

 1876, pi. viii-xi. 



MON xLvni — 05 21 



