A detailed account of the newly designated neotype specimen of Amphiroa crassa Lamouroux (Corallinales, Rhodophyta) is presented. Reasons necessitating its neotypification with a specimen remote from the reported type locality (Shark Bay, Western Australia) are outlined, and historical background information is provided. Brief comparisons with the recently typified type species of the genus, A. tribulus, and with four other Australian species (A. anceps, A. beauvoisii, A. gracilis, A. klochkovana) whose types have been studied in a modern context also are included. A. crassa differs from all of these species in that intergenicula produce a collar of untransformed, calcified peripheral region cells that surrounds and partly to largely encloses each geniculum.