_Pteris Adianti facie, caule ramulis petiolisque politiore nitore nigricantibus, etc._, Gronovius, Fl. Virginica, ed. i., p. 197. Hab.—Crevices of shaded calcareous rocks; from Canada to the Rocky Mountains of British America, and southward to Alabama, Arkansas, Indian Territory and Arizona. It has been found in several parts of Mexico, and even in South America (“Andes of Mecoya, Pearce,” according to _Synopsis Filicum_). It was collected by John Clayton about 1736, “on the shore of the river Rappahannock in a shady place by the root of a juniper near the promontory called Point Lookout,” and I take pleasure in giving it an English name in his honor. Description:—The root-stock of this fern is rather short, usually somewhat nodose, and densely chaffy with very narrow long-pointed soft bright-brown scales, which in the specimens examined are destitute of midnerve. The stalks are rigid and wiry, terete, nearly black in color, but with a slight reddish tinge, and usually more or less pubescent with very narrow chaffy hairs, which are often more abundant and harsher along the rachises, making them almost hirsute. _Pellæa glabella_ was founded on specimens from Missouri and the North-West, which had the stalk perfectly smooth, and the chaff of the root-stock a trifle wider than usual. The section of the stalk shows a single U-shaped fibro-vascular bundle, and a strong outer sclerenchymatous sheath. The fronds are developed late in the Spring, and remain green through the next Winter. They are almost coriaceous in texture, smooth and dark-bluish-green above, paler, and sometimes slightly chaffy beneath. They are from a few inches to about a foot in length, and vary in outline from ovate to oblong-lanceolate. In seedling plants the earliest fronds are round-cordate, the next cordate-ovate, and then follow trifoliate, pinnate, and finally mature bipinnate fronds. The largest fronds have about five pairs of compound pinnæ, each with from three to eleven pinnules, and above these are from four to six pairs of simple pinnæ, besides the terminal one, which is often the longest of all. The pinnules and the simple pinnæ of the sterile fronds are commonly oval, and not more than half an inch long, but those of the fertile fronds are narrower and longer, sometimes nearly two inches long. The base is either truncate or slightly cordate; sometimes where there is a transition from compound to simple pinnæ, a pinna will be found conspicuously auricled on both sides, or on the upper side only. Forked pinnules are occasionally seen.