FLOKA OF LAKOTA OF I'.LACK 11 ILLS. 321 



Jurassic flora, it- is to in' expected that it would survive with niodifieatioiis in the 

 Lower C'rptaeeous. As the descriplicni of tlie ()|-ei;,iii Jurassic plants is uii|)ul>li>iied, 

 of course Ml'. Wiehiiid did iKil ha ve an opjiuil unit \ In compare t lie two, * * * 



Among foreij!;ii specimens presenting analogies, that figured hy 

 Seward as Tdiiiopten's Beyrichii (Sehenkj 8e\v.," from the Wealden of 

 Ke('lesl)otu-ne, bears quite as strong a resemblance to the Black Hills 

 specimens as any form known to me. It is broadei-. and the veins are 

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



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 Ta'tiioiifcris (Oleandridium) Beyrichii (Schenk) Sew." 

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

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

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

 condition seen in characteristic Xilsonias where the laminge extend to 

 the center of the upper surface of the midril) and forms like Tamiopteris 

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

 the prominent midril). 



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

 full.N- illustrated 1)>- Xathorst in four plates, comprising many figures of 

 the beautiftilly 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, Ta^iiopteris, and Oleandridiimi have now (;ome to comprise 

 numerous species of a very generalized and cosmopolitan type of leaf. 

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

 say definitely, in the absence of extended revision, where the one genus 



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

 '' M^m. Mus. Roy. d. Hist. Nat., Vol. I, Bru.xelles, 1900. 

 '" Palaeontograpliii-a, Vol. XIX, p. 221, pi. x.xi.x, figs. 6, 7. 



'' .Natliorst. Bidrag till Sveriges Fo.ss. Fl.: Kongl. Sv. Vet.-Akad., Handliiigar. \ul. XIV, No. 3, Stockholm, 

 I87(), pi. viii-xi. 



.MO.N Xl.VIII — 05 21 



