Homomallium sharpii is described as new based on a specimen col- lected by A. J. Sharp at La Perra, above G6mez Farias, Tamaulipas, Mexico. Most important diagnostic characters of this species are: branches not, or only slightly, homomallous; stem and branch leaves rather well differentiated, and comparatively few subquadrate alar cells (8-13 along the margin in branch leaves). During our study of Mexican hypnaceous mosses, we encountered some specimens of Homomallium which proved to be an undescribed species. It is closely related to H. mexicanum, the only member of the genus presently known from Mexico, but differs in several important characters. We describe it here as new and are pleased to name the species as a tribute to Prof. A. J. Sharp, the collector of the type specimen, who has made many contributions to the botany of Mexico.