185 



morphologically no mid-vein, and when one is present it con- 

 sists of the two inner laterals united, which diverge before reaching 

 the sinus. All this is quite different from the condition in Bau- 

 hinia, with which the fossil accords. 



Habitat. — Miocene shales of Florissant, 1908, The genus 

 occurs as far back as the Cretaceous (cf Berry, Torreya 8 : 218). 



I have sometimes remarked on the absence of Neotropical ele- 

 ments in the Florissant shales. The two plants now described 



Hypolepis coloradensis Ckll. Bauhinia pseudocoiyledon Ckll. 



are apparent exceptions to this, but I believe that they did not 

 invade North America from the south, but belong to a flora 

 which formerly flourished in the north, and has now been pushed 

 southward by changes in the climate. What I mean when I 

 speak of the absence of Neotropical elements at Florissant, is 

 that I do not find genera or families which there is reason to be- 

 lieve originated in South America. Dr. Knowlton, in his inter- 

 esting discussion of the Tertiary flora of the Yellowstone (Monog. 

 U. S. Geol. Surv. XXXII, pt. 2, p. 778) remarks that "the 

 Tertiary flora appears to have originated in the south, while the 

 present flora is evidently of more northern origin." I think that 

 on the contrary, there is much reason for thinking that the Ter- 

 tiary flora originated in the north, and has (so far as it has sur- 

 vived), to a considerable extent, since travelled south. (For a dis- 

 cussion of the same question as applied to animals, see Nature, 

 Aug. 6, 1908, p. 318.) 

 University of Colorado 



