FLORA OF THE SHASTA FORMATION. 225 



plant is the scantiness and imperfection of the material. It ma}^ be 

 described as follows: Frond unknown, sterile form not certainly known. 

 Only portions of the ultimate fertile pinnae or pinnules have been found. 

 Pinnules or lobes in the fruiting forms, almost or quite reduced to short 

 thickened nerves, which bear at their ends large globose or subreniform 

 sori. The leaf substance is very thick and diu'able, so that the plant 

 leaves a thick film of carbonaceous matter on the rock. 



Genus THYRSOPTERIS Kuntze. 



Thyrsopteeis rarinervis Fontaine? 



PI. LXV, Figs. 2-1. 



1889. Thyrsopteris rarinervis Font.: Potomac Flora (Monogr. U. S. Geol. Surv., Vol. 



XV), p. 123, pi. xxvi, figs. 6, 7; pi. xliii, figs. 4, 4a, 6, 6a; pi. xliv, figs. 1, 



la, 2, 5, 5a; pi. xlix, figs. 2, 2a, 2b; pi. clxix, figs. 6, 7. 

 1894. Thyrsopteris rarinervis Font.? in Diller & Stanton: Bull. Geol. Soc. Am., Vol. 



V, p. 450. (PI. LXV, Figs. 3, 4). 

 1895 [1896]. Thyrsopteris rarinervis Font.? in Stanton: Bull. U. S. Geol. Surv., No. 



133, p. 15. (PI. LXV, Figs. 3, 4). 



Several specimens of what seems to be the widely diffused fern 

 Thyrsopteris rarinervis were found. The}^ were obtained at localities Nos. 

 9 and 18. They consist of small portions of penultimate pinnae, carrying 

 pinnules not distinguishable from those of T. rarinervis Font., which was 

 first found in the Lower Potomac of Virginia, in which it is one of the most 

 common ferns. It has since been found in most of the regions of the 

 United States that yield plants of Lower Cretaceous age. The amount of 

 material is not sufficient to justify a positive determination of this plant as 

 Thyrso2)teris rarinervis, and for this reason it is marked as doubtful. 



Family POLYPODIACEiE. 



Genus CLADOPHLEBIS Brongniart. 



Cladophlebis parva Fontaine. 



PI. LXV, Figs. 5-8. 



1889. Cladophlebis parva Font.: Potomac Flora (Monogr. U. S. Geol. Surv., Vol. 



XV), p. 73, pi. iv, figs. 7, 7a; pi. vi, figs. 1, la, 2, 2a, 3, 3a. 

 1894. Cladophlehis inclinata Font.? in Diller & Stanton: Bull. Geol. Soc. Am., 



Vol. V, p. 450. (PI. LXV, Fig. 8.) 



MON XLVIII — 05 15 



