88 STUDIES IN GEOLOGY, No. i 



Polystichum difficulties are almost unsurmountable for 

 several reasons namely, the inadequate amount of fossil 

 material, the variability of the recent species, the lack of 

 sufficient comparative material, and the difficulty of con- 

 necting mere names of recent species with actual specimens. 



Polystichum is a large genus in the existing flora found 

 on all the continents, and hence with a cosmopolitan distribu- 

 tion. It contains many vague or but little understood species 

 and many extremely variable and polymorphous forms. It 

 is found in both the tropical and boreal regions (Greenland, 

 Antarctica) and on many high mountains, and its present 

 distribution is clearly indicative of a long geological history 

 which is almost entirely unknown. 



Maxon, in a recent revision x of the West Indian species, 

 recognizes 19 species in that region. He has been good 

 enough to examine the fossil for me and considers it an ally 

 of the historic and extremely variable Polystichum trian- 

 gulum (Linnaeus) Fee. The latter, as far as known, is now 

 strictly West Indian in its distribution. In Jamaica it is 

 common in rocky situations up to 1,800 meters. Other West 

 Indian species whose pinnules are more or less closely 

 similar to the fossil are the Cuban species Polystichum 

 decoratum Maxon, Polystichum heterolepis Fee, and the 

 Jamaican Polystichum rhicaphorum (Jenman) Maxon. 



There are a number of existing species in South America, 

 some ranging from the Antilles into Brazil and others rang- 

 ing from Central America into the Andean region, while 

 still others are confined to South America. I have examined 

 specimens of Polystichum ftexum (Kuntz) Phillippi, from 

 Juan Fernandez, Polystichum capcnse (Willdenow) J. 

 Smith, from Chile and Polystichum mohrioides (Bory) 

 Presl from the Falkland Islands. These, while they show 

 the generic likeness of the fossil, are not specifically close 

 to it. Of the three the last is most like the fossil, but it is 



1 Maxon, W. R,, Contr. U. S. Natl. Herb., Vol. 13, pt. i, 1909, 

 PP. 25-39, pis. 2-9. 



