290 MESOZOIC FLORAS OF UNITED STATES. 



midrib and supported on short laminee that are so much modified that 

 the_v are reduced to thickened veins. This form, in the large sori and 

 short stout pedicels carrying them, is even more like Heer's Dicksonia 

 clavipes than the fertile forms of D. inontanensis. PI. LXXI, Fig. 8, 

 gives a portion of this magnified to show the sori, which, belonging 

 to a Dicksonia, have their valves closed and showing their outer sur- 

 face. PI. LXXI, Fig. 9, represents a somewhat different fragment of 

 a fertile pinnule, which has also large sori on short supports. But 

 these latter are more foliaceous than those shown in Fig. 7, and have 

 on each side of the nerve which bears the sori at its summit a wing 

 formed by a remnant of the lamina of the pinnule, giving a form appar- 

 ently not so much altered from the sterile pinnule as is that figured 

 in Fig. 7. This wing, however, is thickened and gives with the sorus 

 a club-shaped or spatulate form. Fig. 10 gives a portion of this mag- 

 nified. Fig. 11 represents the small specimen collected by Mr. Weed 

 at the Gilt Edge coal mine in the Judith Mountains, about 50 miles 

 east of the place where most of the other specimens were obtained. Its 

 chief importance is due to the fact that it was upon this specimen that 

 the author founded the species. 



The plant occurs in both Professor Ward's and Mr. Weed's 

 collections. 



Genus THYRSOPTERIS Kuntze. 



TiiYRSOPTERis ELLIPTIC A Fontaine. 

 PI. LXXI, Figs. 12, 13. 



1889. TJiyrsopteris elliptica Font.: Potomac Flora (Monogr. U. S. Geol. Surv., 



Vol. XV), p. 133, pi. xxiv, figs. 3, 3a; pi. xlvi, figs. 1, la; pi. 1, figs. 6, 6a, 9; 



pi. li, figs. 4, 6a, 6b; pi. liv, fig. 6; pi. Iv, fig. 4; pi. Ivi, figs. 6, 6a, 7; pi. Ivii, 



figs. 6, 6a; pi. Iviii, figs. 2, 2a. 

 1898. TJiyrsopteris elliptica Font.? in Weed & Pirsson: Eighteenth Ann. Rep. U. S. 



Geol. Surv., 1896-97, Pt. Ill, p. 482. (Pi. LXXI, Fig. 13.) 



Two specimens of a fern apparently identical with Thyrsopteris 

 elliptica, a characterisic plant of the Lower Potomac of Virginia, were 

 found, one by Mr. Weed at the Grafton locality and the other by Pro- 

 fessor Ward near Geyser. The latter is figured in PL LXXI, Fig. 12, 

 and the former in Fig. 13. They are fragments of ultimate pinnae, 

 but contain pinnules sufficiently M^ell preserved to leave little doubt 

 that they belong to the Potomac plant. 



