Abstract
A taxonomic study on the marine diatoms from the southwestern coast of Puerto Rico is reported. One family, Chaetoceraceae, of the suborder Biddulphiineae, with 2 genera, 31 spp. and 1 variety were observed. Eight out of 32 taxa are cited for the first time for Puerto Rico. These are: Bacteriastrum comosum; B. furcatum; B. mediterraneum; Chaetoceros anastomosans; C. dadayi; C. debile; C. eibenii and C. neogracile. One species is new for Puerto Rico and the Caribbean Sea, Chaetoceros filiferum. Most of the identified species are cosmopolitan in temperate-tropical waters and neritic.