286 MESOZOIC FLORAS OF UNITED STATES. 



surprisingly small. From the collections made in the Great Falls coal 

 field that I have examined I get the impression that this feature is char- 

 acteristic of the flora of that field also, for apparently even large collections 

 yield only a few species, these having many specimens. I find here 

 again illustrated a fact observed before: I have noticed that any layer 

 that contains a large amount of Equisetum shows very little of other 

 identifiable plants. Equisetum, in some of the laj^ers of shale from the 

 Geyser locality, is exceedingly abundant, and in the same layer other 

 species that can be made out are rare. 



DESCRIPTION OF THE SPECIES. 



PhyKim PTERIDOPHYT^ (Ferns and Fern 



^^llies). 



Order FILICALES (Ferns). 



Family CYATHEACEiE. 



Genus DICKSONIA L'Heritier. 



DiCKSONiA MONTANENSis Fontaine n. sp. 



PI. LXXI, Figs. 1-4. 



Of this plant only fructified forms were found. The frond was 

 probably tripinnatifid at least, as the largest portions found seem to 

 be pinnae belonging to larger parts of the frond. The rachis of the 

 principal pinnae seen is comparatively stout and rigid, and in the less 

 modified forms, such as are depicted in PI. LXXI, Fig. 1 (of which an 

 enlarged pinnule is shown in Fig. 2), is almost winged by the decurrent 

 leaves of the ultimate pinnae.' The pinnae of the ultimate order vary 

 somewhat in the degree of their modification to assume the fertile form. 

 Some, as the specimen figured in PI. LXXI, Fig. 1, seem to l^e more 

 foliaceous and less metamorphosed. , These are the broadest forms that 

 were found. They are decurrent on their lower side so as almost to 

 form a wing on the principal rachis. The lower laciniae next to the 

 principal rachis are more united and more foliaceous than the upper ones 

 and appear to have the sori less well developed. These pinnae go off from 

 the main rachis at an angle of about 4.5° and then turn strongly away 

 from it, so as to stand nearly at right angles to it. They are oblong- 



