Southward, A.J. (2008). Barnacles: keys and notes for the identification of British species. Synopses of the British fauna (new series), 57. Field Studies Council: Shrewsbury, UK. ISBN 978-1-85153-270-4. viii, 140 pp. (look up in IMIS) [details]
illustrated by Darwin (1854), total length can be up to 25 mm