Rissoa membranacea. Apical angle (1) c. 35º. Subsutural collar (2). Body whorl (3) c. 60% H.. Periphery smoothly rounded (4). White, labial varix (5). Thin, flared palatal lip (6). D-shape aperture c. 40% of shell height (7). Adapical angle c. 65º (8). Everted/flared peristome around aperture reflected onto body whorl in columellar (9) and parietal areas (10). Brown band (11) between the varix and lip externally and internally. 1 to 11: adult H. 9.5 mm & 14: juvenile with angled periphery, Orkney, April 2018, leg. I. Williamson and 12: H. 5.7 mm, Galway, Ireland, September 2002. Leg. J. Fisher, coll. S. Taylor. 13 Rissoa parva adult with rounded periphery.