Plants 4.5--7 mm, dark olive green. Stem leaves oval to ovate-lanceolate, 1.1--1.9 ´ 0.4--0.7 mm, margins incurved distally, apex plane, awn 0.1--1.1 mm, lamina 2-plicate, plications not always reaching base; distal laminal cells 2-stratose; medial laminal cells 1-stratose; juxtacostal basal laminal cells quadrate to long-rectangular, 20--47 ´ 8--12 µm, evenly thick-walled; marginal basal laminal cells quadrate to rectangular, 12--34 ´ 6--12 µm, thin or thick end walls and thin lateral walls. Sexual condition dioicous. Seta 0.8--1.2 mm. Capsule emergent, ovate to campanulate; peristome present, cribrose, hygrocastique.

Acidic, dry sandstone, shale, and granitic boulders and bedrock exposures but also found on volcanic outcrops and granodiorites; 0--3300 m; Greenland; Alta., B.C., Labr., Nfdl., N.W.T., Nun., Ont., Que., Yukon; Alaska, Ariz., Colo., Maine, N.Mex., N.Y., S.Dak., Tenn.; Eurasia.

Coscinodon cribrosus is an uncommon moss known from widely disjunct sites across North America. It has been suggested that this distribution is due to a restricted occurrence on mineral rich rocks. The sites from Ellesmere Island, Tennessee, Colorado, South Dakota, Thunder Bay and Alaska support this contention as they are all reported to be either heavy metal or copper-bearing deposits or the specimens are associated with the "copper-moss," Mielichhoferia mielichhoferi. However, specimens in other areas have been collected on sandstones and shales. The species appears to be largely controlled by the extent of the Cretaceous epicontinental seaway that flooded much of central North America from the Gulf of Mexico to the Yukon (R. I. Hastings 1999). The species does not occur within the boundaries of the seaway except on isolated granodiorite outcrops that were exposed subsequent to the retreat of the seaway. C. cribrosus is recognized by its 2-plicate, 2-stratose leaves with incurved margins and emergent capsule with a well-developed cribrose peristome. It is the only species of Coscinodon that has a hygrocastique peristome, i.e. its peristome opens when wet and is closed when dry.