118 PROCEEDINGS OF THE NATIONAL MUSEVM. vol.54. 



pinnule. The venation is largely immersed in the thick lamina. At 

 the base three veins diverge at acute angles of about 20° on one side 

 and 30° on the other, the lateral ones ending in the tips of the lateral 

 lobes and the median one in the tip of the pinnule. A few subordinate 

 dichotomously forking veinlets are faintly seen. On subordinate 

 branches from these three primary veins on each side are impressions 

 of round sori with a slightly raised center, about 0.25 mm. in diameter. 



This fern is very obviously a species of Polystichum, the characters 

 of which as a whole are very well known. When it comes to making 

 comparisons with existing species of 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 connect- 

 ing 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 distribution. 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 moun- 

 tains, and its present distribution is clearly indicative of a long geo- 

 ogical history which is almost entirely unknown. 



Maxon, in a recent revision ^ 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 triangulum (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 rhizophorum (Jenman) 

 Maxon. 



There are a number of existing species in South America, some rang- 

 ing from the Antilles into Brazil and others ranging from Central 

 America into the Andean region, while still others are confined to 

 South America. I have examined specimens of Polystichum Jlexum 

 (Kuntz) PhilMppi, from Juan Fernandez, Polystichum capense 

 (Willdenow) J. Smith, from Chile and Polystichum mohrioides (Bory) 

 Presl from the Falkland Islands. These, while they show the 

 generic fikeness of the fossil, are not specifically close to it. Of the 

 three the last is most like the fossil, but it is more dissimilar than the 

 West Indian species previously enumerated. Other existing South 

 American species which I have not seen include Polystichum dubium 

 (Hooker) Diels of the Andes of Ecuador and Peru, which is markedly 

 different from the fossil in its pinnate and anastomosing veinlets 



Maxon, W. K., Contr. U. S. Natl. Herb., vol. 13, pt. 1, lECt.pp 25-39, pis 2-9. 



