3 literature references for Smittina rigida Lorenz, 1886:

Title: ITIS database
Author: Brunel, P., L. Bosse, and G. Lamarche.
Year: 1998
Title: Catalogue of the marine invertebrates of the estuary and Gulf of St. Lawrence. Canadian Special Publication of Fisheries and Aquatic Sciences, 126. 405 p.
Author: Hayward, P.J.
Year: 2001
Title: Bryozoa, in: Costello, M.J. et al. (Ed.) (2001). European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: