Crangonyx grandimanusBousfield, 1963, a relatively large stygobitic amphipod endemic to the Floridan aquifer, is redescribed from its holotype specimen and topotype material. In addition to the morphological redescription, genetic sequence data for sections of the nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA are provided from the examined topotypes. The erratum for this article can be found in Bulletin of the Peabody Museum of Natural History, Vol. 60 No. 1.