Biologia Centrali-Americana London, 1879-1915, archaeology, botany, Central America, description and travel, scientific expeditions, zoology, 34, shells, mollusc, This illustration presents detailed anatomical studies of two distinct bivalve species, showcasing their unique shell structures. The top portion illustrates a specimen labeled as 'Unio tampicoensis,' featuring a smooth, elongated shell with subtle ridges and a detailed view of its internal anatomy. The bottom section depicts 'Panucoensis,' characterized by a more rounded shell with pronounced growth lines. Each specimen is meticulously rendered, highlighting the curvature and intricate patterns on their surfaces. The labeling of specific parts emphasizes the biological diversity and structural complexity of these freshwater mollusks.