4 bivalve species that look like brother and sister.

Katelysia (Textivenus) texta (Lamarck) 3 on the left at the top. Callocardia (Nitidavenus) nitidula (Lamarck 1806). The lone one at the upper right. Nemocardium (Nemocardium) paueri (Guembel) 4 in the middle and 2 bottom left. Glycimeris alpinus (Mayer) 2 bottom right. From St. Pankraz, Salzburgerland, Austria. Fossilschicht, Lutetian, middle Eocene.