From various lines of evidence, including handwriting, contemporary correspondence, and study of herbarium specimens, the holotype of Grevilleanum serratum, the name of a moss that dates from 1826, is shown to be a specimen in the Bryophyte Herbarium of the New York State Museum. The holotype of G. serratum is identical taxonomically to Timmia megapolitana Hedwig (1801), making the former name a taxonomic synonym of the latter. The bryological contributions of the authors of G. serratum, L. C. Beck and E. Emmons, are discussed. Beck’s bryophyte herbarium, mentioned as the foundation of an evidently completed but unpublished early moss flora of the United States, has been located largely intact but unrecognized as such in the collections of the New York State Museum. Ebenezer Emmons, remembered today mainly for his significant contributions to stratigraphic geology, had only a passing interest in mosses; Lewis Beck, in contrast, worked extensively on mosses between about 1825 and the 1830s, although the results of his studies were largely unpublished.