This is a vintage scientific illustration, specifically a cyanotype plate depicting various diatoms. The plate is labeled "PLATE III." and numbered "113" in the upper right corner. It features 23 numbered diatom specimens arranged across a cream-colored background. The diatoms are depicted as circular or oval shapes, each covered in intricate patterns of dots and lines, creating a textured, microscopic view. The patterns vary between specimens, showcasing the diversity of diatom structures. Some diatoms are complete circles, while others are fragmented or half-circles. The color scheme is predominantly a muted blue, characteristic of cyanotypes. The background is a light cream color, providing contrast to the blue diatoms. There is text at the top of the plate reading "A. Schmidt's Diatom.-Atlas." and at the bottom, a small inscription. The overall aesthetic is reminiscent of a vintage scientific textbook or botanical illustration.