332 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



ONYCHIOPSIS LATILOBA (Fontaine). 



Sphenopteris laliloba Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 1890, p. 90, pi. 



35, figs. 3-5; pi. 36, figs. 4-9; pi. 37, fig. 1.— Fontaine, in Ward, Monogr. U. S. 



Geol. Surv., vol. 48, 1906, pp. 281, 479, 491, 511, 534, 557. 

 Thyrsopteris brevipennis Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 1890, p. 124, 



pi. 34, fig. 3; pi. 36, fig. 2; pi. 37, figs. 3, 9; pi. 38, fig. 1; pi. 41, fig. 4.— 



Fontaine, in Ward, 19th Ann. Rept. U. S. Geol. Surv., pt. 2, 1899, p. 662, 



pi. 162, fig. la. 

 Thyrsopteris divaricata Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 1890, p. 125; 



pi. 37, figs. 5-8; pi. 70, fig. 1.— Fontaine, in Ward, Monogr. U. S. Geol. 



Surv., vol. 48, 1906, pp. 504, 511, 517, 521. 

 Thyrsopteris crenata Fontaine, Monogr. U. S. Geol. Surv., vol. 15, 1890, p. 127, 



pi. 39, figs. 1, 2. 



Description. — Frond large tripinnate; principal rachis very stout 

 sometimes winged. Leaf -substance thin but coriaceous. Primary 

 pinna? opposite or subopposite with a stout, rigid, rachis, which is 

 often somewhat flexuous; ultimate pinnae remotely placed, very 

 short, decurrent, passing toward the summit of the principal pinnae 

 or of the frond through lobed pinnules into entire ones. Pinnules 

 somewhat remotely placed, cuneate at base, those in the lower part 

 of the frond cut more or less deeply into oblong acute to obtuse lobes, 

 passing toward the tips of the ultimate pinnae into lobed pinnules 

 like those of the upper part of the frond, and at the tips into ovate 

 or oblong lobes and teeth. In the upper part of the frond they are 

 elliptical, three lobed, or entire. All the pinnules and segments are 

 broad. The ultimate pinnae and the pinnules of the lower part of 

 the frond usuall}' terminate in three lobed segments or in broad 

 elliptical pinnules. The veins are copiously branched, diverging 

 flabellately into the lobes and teeth, and are very distinct and strong, 

 although not coarse. 



This is a fine, large species, probably arborescent, and quite dis- 

 tinct from the other species of Onychiopsis. It is common through- 

 out the Potomac but rather less abundant in the Patapsco forma- 

 tion than in the older beds. It has been recorded from the Lakota 

 formation in the Black Hills area and from the Kootenai formation 

 in both Montana and British Columbia. There is some variation 

 exhibited by the various forms referred by the writer to this species, 

 and some of the smaller ultimate pinnae are readily confused with 

 other species of Onycliiopsis. 



Occurrence. — Patuxent formation: Fredericksburg, Dutch Gap, 

 Telegraph Station (Lorton), Virginia; New Reservoir (?), District 

 of Columbia. Arundel formation: Langdon (?), District of 

 Columbia; Bewley estate (?), Bay View (common), Maiyland. 

 Patapsco formation: Deep Bottom, Mount Vernon, Hell Hole (?), 

 Chinkapin Hollow (?), Virginia; Federal Hill (Baltimore), Maryland. 



Collections. — United States National Museum, Johns Hopkins 

 University, Goucher College. 



