One of the most striking features in the zoological history of the Mississippi basin is the exceedingly rich and varied moluscan fauna, which is characterized particularly by the Unio family, including all the common river mussels. The great abundance of individuals, the large number of forms and the wide geographic range of many of the varieties has perhaps no parallel elsewhere. The first of these statements requires no further proof to one who has worked anywhere within the limits of the region under consideration. The second proposition finds ample evidence in collections of more than sixty different kinds of these mollusks from a single locality. Altogether more than seven hundred species of the family Unionidae have been described from North America-over four-fifths of the entire number known to exist in the world. Having such a large number of closely related forms to deal with, it has become very convenient, and indeed very necessary, to separate the chief genus into a number of subordinate groups, naming each after its leading species; thus the sections are known as the "gibbosus," "undulatus" groups, etc.
Proceedings of the Iowa Academy of Sciences
©1893 Iowa Academy of Science, Inc.
Keyes, Charles R.
"Derivation of the Unione Fauna of the Northwest,"
Proceedings of the Iowa Academy of Science, 1(Pt. 4), 25-29.
Available at: https://scholarworks.uni.edu/pias/vol1/iss4/11