Originally published by the Illinois Natural History Survey in 1992 as Manual 5, the electronic version of this field guide by Kevin Cummings and Christine Mayer is worth the visit. The guide contains an introduction to mussels (biology and economic importance), a brief summary of the conservation status of mussels, a glossary of terms, and a simple key to freshwater bivalves. The heart of the site, however, is the species accounts section, covering the subfamilies Cumberlandinae, Ambleminae, Anodontinae, and Lampsilinae. Each species account includes a color photograph and physical description, key characteristics, a description of habitat requirements and conservation status, and a black-and-white map of the species' distribution in the Midwest. Of added utility are the links (where applicable) pointing to similar-looking species.