Adult specimens of Boettgerilla pallens from Europe. The specimen in the upper photograph (from Upper Lusatia, eastern Germany) is about 40 mm long. The lower photograph is a slightly dorsal view of a specimen freshly preserved in alcohol, where the scale has 1 mm divisions (collected from Leigh Delamere Motorway Services, Wiltshire, England). The keel here shows up most clearly where kinked near the tail, but it continues up to the mantle.
Wolfgang Junius took the upper photograph.