Bryol. Eur. 1: fasc. 33/36. 1846. -- Bryum fulvellum Dicks., Pl. Crypt. Brit., Fasc. 4, 10. 1801. -- Arctoa blyttii (Dicks.) Loeske, Stud. Morph. Syst. Laubm. 86. 1910.
Plants in rather dense, lustreless, dark green to green turfs, tufts or cushions, to 15 mm high. Leaves only obscurely falcate secund, erect spreading when moist, somewhat crispate when dry, grooved distally but not sharply keeled, not fragile. Larger stem leaves to 4 mm long, with an ovate to obovate, sheathing base which more or less gradually contracts to a linear and setaceous acumen comprising up to 4/5 of total leaf. Lamina cells of leaf limb in 1–4 rows, quadrate, to 10 µm wide, prorate-papillose to high mammillose, especially near leaf apex. Median cells of sheathing base smooth, to 12 µm wide, 3–5: 1, in regular rows, rectangular, not at all pitted. Marginal cells of leaf base not differentiated. Alar cells moderately to not at all demarcated, not extending to costa, rectangular and brownish, to 15 µm wide, not inflated, thin walled. Costa diffuse near base, becoming well demarcated in the distal 1/2 of the expanded leaf base, long excurrent and occupying nearly all of the awn. Costa cross-section homogeneous, with walls only moderately thickened. Margin plane to erect, entire throughout or more commonly slightly serrulate near apex. Rhizoids red-brown, to 12 µm wide at base, smooth, sparsely produced and restricted to the stem base. Stem cross-section nearly homogeneous but with a poorly defined central strand, with even the outer cortical cells rather large, but somewhat pigmented.
Autoicous with perigonia on branches inserted near the base of the perichaetial stem. Perichaetial leaves loosely sheathing only the base of the seta, larger than but otherwise similar to the adjacent vegetative leaves. Monosetous with the seta to 8 mm, yellow to brownish, straight and smooth. Urn to 2 mm long, inclined and arcuate, about 2: 1, wrinkled to somewhat sulcate when dry, strumose. Operculum rostrate, about 2/3 as long as the urn. Exothecial cells to 20 µm wide, to 2.5: 1, irregular in size and shape, not in vertical rows, polygonal with neither the lateral nor the end walls parallelling one another, thin-walled. Exothecial cells near mouth of capsule isodiametric and reduced in size, in 2–4 rows; these cells continuing on operculum but abruptly differentiated on beak into much elongated cells. Annulus in several rows, deciduous. Peristome red-brown, inserted near capsule mouth, erect when dry, to 500 µm long, bifid nearly to middle, lanceolate but with the distal portion of each division filiform and hyaline. Dorsal plates of peristome vertically striate but ventral plates and peristome apex papillose. Spores spherical, minutely papillose, to 18 µm.