Nautilocaris saintlaurentae gen. nov., sp. nov., is described and illustrated from hydrothermal vents in the North Fiji Basin and Lau Basin in the south-western Pacific. This new taxon is assigned to the Alvinocarididae. It has a well-developed, dorsally dentate rostrum, carapace with pterygostomian spine present, eye broadly fused mesially, epipod–setobranch complex present above pereopods, and appendix internae on second to fourth pleopods greatly reduced. This combination of characters places it in an intermediate position between a group of species in the genus Alvinocaris with well developed, dorsally dentate rostrum, carapace with pterygostomian spine present, eyes narrowly fused mesially, epipod–setobranch complex absent and well-developed appendices internae on second to fourth pleopods, and Mirocaris fortunata with rostrum unarmed, carapace with rounded pterygostomian angle, eye broadly fused mesially, epipod–setobranch complex present above pereopods and appendices internae on second to fourth pleopods greatly reduced. The habitat of the new species is briefly described.