caption: The image shows a group of four clams on a black background with the text "Unio Perdix Lea, 1834, Lectotype USNM 84857" written on them. The clams are arranged in a symmetrical pattern, with the largest clams in the center and two smaller clams surrounding it. The shells are a light brown color with a glossy sheen, and the text is written in a bold white font.