Specimens of Hormophysa cuneiformis ( J. Gmelin) P. Silva, collected by R. E. DeWreede in July 1968 and by the author in January 1971 from Palau, are documented for the first time and represent the first collections of a member of the family Cystoseiraceae from Micronesia. A single specimen 6 cm tall of H. cuneiformis was collected 4.5 yr later in July 1975 on a reef bench tide pool at Pagan Island in the Northern Mariana Islands by R. Rechebei and was reported in a floristic account of the Chlorophyta and Phaeophyta of the Northern Mariana Islands in 1977. Specimens of this large and conspicuous brown alga have not been reported previously from Palau nor other islands in Micronesia.