We present transcriptomic data from eight specimens of two flat periwinkles species (L. fabalis and L. obtusata) . These resources will facilitate evolutionary studies, including the role of adaptive introgression and reinforcement in the diversification of flat periwinkles, producer-herbivore interactions, as well as the identification of genomic regions involved in key traits that diverged between rough and flat periwinkles (e.g. adaptation to live on a rocky substrate versus macroalgae, respectively).