Natural history museum collections provide a biodiversity window into the past and are of particular importance to the study of extinction-impacted clades such as the Pacific Island tree snail family Partulidae. Deliberate introduction of the predatory rosy wolf snail Euglandina rosea in the late 20th century led to the extinction/extirpation of 55/61 Society Island Partulidae species. In this study, we phylogenomically investigated the inter-relationships of the three surviving Society Island valley Partula species: P. taeniata (Moorea), P. clara and P. hyalina (Tahiti). All three formed a distinct clade in earlier mitochondrial phylogenies. Using Next Generation Sequencing (NGS) double digested Restriction Associated DNA sequencing (ddRADseq), we found that 46-year-old lyophilized museum specimens produced similar numbers of reads, sequencing depth, and loci as 10-year old ethanol-preserved collections. Phylogenomic trees indicated that Tahitian P. clara and P. hyalina are the result of a single founding lineage from Moorea, contrasting previous mitochondrial results and clarifying the enigmatic taxonomic status of P. c. incrassa. Our study highlights the utility and viability of NGS techniques for museum specimens and their increased resolution of evolutionary patterns. Sampling will be expanded to include the remaining Society Island partulid taxa to further explore the evolutionary history of this radiation.