Work found, with species-group names introduced therein:
Forbes, E. and S. Hanley. 1850b. A History of British Mollusca, and their Shells. A History of British Mollusca 3 pp. 1-320, pls. EE, GG-HH, JJ-LL, OO-PP, XX, 75-76, 80-93, 115-121. John van Voorst: London. Litorina tenebrosa var. intermedia, see Littorina saxatilis (Olivi, 1792)