668 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



lobes or pinnules consisting of a strong midnerve passing to the tip, and 

 6 or 8 pairs of alternate once-forked lateral nerves; fruit dots not seen. 



This large and striking species is the most abundant fern found in the 

 Park. It is represented in the collection by fully 40 specimens, all from 

 one locality. The largest example (fig. 7) is 17.5 cm. long and 2.5 cm. 

 broad, and still lacks the terminal portion. It has a stipe 8 mm. long and 2 

 mm. thick. Fig. 5 is 16 cm. long and 23 mm. broad, and lacks both base 

 and apex. Some of the fronds must have been fully 25 cm. long. 



This species is well characterized. It has a thick grooved rachis (1mm.) 

 and a short thick stipe. The lobes or pinnules are irregularly ovate, sepa- 

 rated usually to the middle by a sharp sinus, and having a sharp upward- 

 pointing apex. The nervation consists of a strong midnerve ending in the 

 apex and about 7 pairs of alternate forked branches. As in the former 

 species, the lower nerves of adjacent lobes unite and pass upward to the 

 sinus. Occasionally there may be an unforked nerve, but it is the exception. 



This species is associated in the same beds with A. iddingsi and much 

 resembles it, differing, however, in having apparently simple fronds that 

 are uniformly larger than the pinna? of the former species, and in having 

 the nervation of the lobes always forking (see fig. 8 and 8a). It differs 

 further in having a short stipe and in having the upper portion nearly or 

 quite entire. 



The correctness of this generic reference is of course a matter of more 

 or less doubt, as no fruiting specimens have been found, but the fern appears 

 to be allied generically at least to A. iddingsi. It is certainly a well-marked 

 species for geological purposes. 



Habitat: Yellowstone River, one-half mile below mouth of Elk Creek, 

 Yellowstone National Park, at base of bluff; collected by F. H. Knowlton, 

 August, 1888. 



ASPLENIUM EROSTJM? (Lx.) Kll. 



PI. LXXX, fig. C. 



Asplenium erosum (Lx.) Kii. : Bull. U. S. Geol. Surv. No. 152, p. 45, 1898. 

 Pteris erosa Lx.: Tert. PI., p. 53, PI. IV, fig. 8. 



This appears to be the same as described by Lesquereux, but is obscure 

 and difficult to make out. None of the specimens are complete, and all have 

 the nervation very poorly preserved. The margin seems more erose than 



