280 Systematic Paleontology 



Thyrsopteris oMusilo'ba Fontaine, 1890, Mon. U. S. Geol. Surv., vol. xv, 



1889, p. 143, pi. Iviii, figs. 7, 10. 

 Thyrsopteris crassinervis Fontaine, 1899, in Ward, 19th Ann. Rept. U. S. 



Geol. Surv., pt. ii, p. 658, pi. clxi, figs. 3, 4. 

 Thyrsopteris pecopteroides Fontaine, 1899, Ibid., p. 661, pi. clxi, figs. 16-19. 

 Adiantites parvifoUus Fontaine, 1906, in Ward, Mon. U. S. Geol. Surv., vol. 



xlviii, 1905, p. 558, pi. cxvii, fig. 1. 

 Thyrsopteris ?iervosa Fontaine, 1906, in Ward, Mon. U. S. Geol. Surv., vol. 



xlviii, 1905, pp. 511, 517, 519, 521, 528, 548, 571. 

 Thyrsopteris Meekiana Fontaine, 1906, in Ward, Mon. U, S. Geol. Surv., 



vol. xlviii, 1905, pp. 519, 565; pi. cxix, fig. 1. 

 Thyrsopteris crassinervis Fontaine, 1906, in Ward, Mon. U. S. Geol. Surv., 



vol. xlviii, 1905, pp. 513, 528, pi. cxii, figs. 5, 6. 

 Onychiopsis nervosa Berry, 1911, Proc. U. S. Natl. Mus., vol. xli, p. 327. 



Description. — Frond bipinnate or tripinnate. Principal rachis medi- 

 uinly stout, somewhat flexnous, sometimes winged in the upper part. 

 Pinnae alternate or subopposite, ovate to ovate-lanceolate in outline, be- 

 coming entire apically, the pinnules passing into dentate teeth while the 

 ultimate pinnae become dentate pinnules. This character renders distal 

 fragments quite different in appearance from the normal form of this 

 species, and quite like Clad a phi eh is. In some individuals the pinnse 

 lower down on the frond assume this form, constituting the supposed 

 species Thyrsopteris crassinervis of Professor Fontaine and well shown 

 in the specimens figured from Chinkapin Hollow and near Glymont. 

 Every gradation is shown, however, between this type and the usual type 

 of pinhse made up of alternate, very oblique, decurrent pinnules, usually 

 rather deeply cut into subrliombic basal lobes which become ovate or 

 elliptical lobes, and finally teeth in passing distad. Base contracted, 

 subpetiolate. Veins numerous and slender, but very distinct, branching 

 obliquely, flabellate, repeatedly forked, subparallel. Texture coriaceous. 



While the fragments of the fronds of this species are all small the 

 plant which bore them must have been of quite considerable dimensions. 

 Representative material is readily distinguished from the other species 

 of Onychiopsis recognized, but small fragments are liable to confusion 

 with Onychiopsis hrevifolia, in fact Professor Fontaine founded no less 

 than six nominal species upon such fragments, all of which are believed 

 by the writer to represent slight variations of a single species. 



