Plants 7.0--10.0 mm, olive green. Stem leaves ovate to ovate-lanceolate, 1.4--2.4 ´ 0.4--0.7 mm, margins plane or one margin revolute at mid-leaf, apex plane, awn 0.4--1.4 mm, lamina non-plicate; distal laminal cells 1-stratose; medial laminal cells 1-stratose; juxtacostal basal laminal cells long-rectangular, 15--80 ´ 7--10 µm, evenly thin-walled; marginal basal laminal cells quadrate to long-rectangular, 16--60 ´ 7--15 µm, thin or thick end walls and thin lateral walls. Sexual condition autoicous. Seta 1.4--2.4 mm. Capsule exserted, cylindrical, commonly constricted at rim; peristome present, solid, xerocastique.

Most common on dry sandstone and granitic boulders and bedrock exposures but also limestone and volcanic outcrops; 300--3000 m; Alta., B.C.; Ariz., Calif., Colo., Idaho, Minn., Mont., Nev., N.Mex., Oreg., S.Dak., Utah, Wash., Wis., Wyo.; Asia (Armenia, Kazakstan, Pakistan).

Coscinodon calyptratus is common and widespread in the dry interior mountain areas of western North America. To the east it is largely bounded by the front ranges of the Rocky Mountains and acidic outliers such as the Black Hills of South Dakota. Two disjunct sites in Wisconsin and Minnesota define the eastward extent of the species. It is not found along the west coast mountains. The species is endemic to North America. Specimens reported from central Asia and New Zealand by J. Muñoz (1998) are in error. The former is an undescribed species of Coscinodon and the latter is a Grimmia.

The non-plicate, 1-stratose leaves with plane or one revolute margin, and exserted capsule, clearly separate this species from all other North American Coscinodon. The autoicous sexual condition of this species is unique for the genus but is often difficult to ascertain on any particular specimen. This species is most commonly confused with Grimmia longirostris (formerly G. affinis) than any other species of Coscinodon. Both species are autoicous, have a similar robust habit, have leaves that are strongly keeled and may have recurved margins and have long exserted capsules. If fertile and with capsules the species are easily distinguished as C. calyptratus has large, plicate calyptra and has a thin-walled filmy annulus. In contrast, G. longirostris has smaller, smooth calyptra and a large, prominent annulus. Gametophytically C. calyptratus has 1-stratose areolation across the distal and medial lamina except for a 2-stratose margin. Its basal cells tend to be evenly thin-walled. Grimmia longirostris has a 2-stratose distal lamina and a wide 2-stratose margin at mid-leaf. Its basal cells tend to be thicker walled.