A new species of Websterinereis Pettibone, 1971, Websterinereis pettiboneae sp. n. is described from La Paz Bay, Gulf of California, Mexico. This species is similar to Websterinereis foli (Fauvel, 1930) in the neuropodial falcigers shape, but can be separated by the tentacular cirri length, notopodial prechaetal lobe shape, and the size of the notopodial dorsal and ventral ligules on posterior parapodia. Websterinereis foli is redescribed based upon type material. Additional observations on the inter-annual density variation of Websterinereis pettiboneae sp. n. during a four-year study are also provided. A key to all species of Websterinereis is included.