1. Species Io fluvialis (Say, 1825)
2. Subgenus Io (Elimia) H. Adams & A. Adams, 1854 accepted as Elimia H. Adams & A. Adams, 1854 (original rank)
3. Species Io angitremoides C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
4. Species Io brevis J. G. Anthony, 1860 accepted as Io fluvialis (Say, 1825) (junior synonym)
5. Species Io clinchensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
6. Species Io fasciolata Reeve, 1860 accepted as Lithasia duttoniana (I. Lea, 1841) (junior synonym)
7. Species Io fluviatilis auct accepted as Io fluvialis (Say, 1825) (unjustified emendation)
8. Species Io funiculata Reeve, 1860 accepted as Elimia impressa (I. Lea, 1841)
9. Species Io fusiformis I. Lea, 1831 accepted as Io fluvialis (Say, 1825) (junior synonym)
10. Species Io gibbosa Reeve, 1861 accepted as Io fluvialis (Say, 1825) (junior synonym)
11. Species Io gracilis I. Lea, 1862 accepted as Pleurocera prasinata (Conrad, 1834) (junior synonym)
12. Species Io inermis J. G. Anthony, 1860 accepted as Io fluvialis (Say, 1825) (junior synonym)
13. Species Io loudenensis Goodrich, 1940 accepted as Io fluvialis (Say, 1825) (junior synonym)
14. Species Io loudonensi C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825)
15. Species Io loudonensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
16. Species Io lurida Reeve, 1861 accepted as Io fluvialis (Say, 1825) (junior synonym)
17. Species Io lyttonensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
18. Species Io modesta I. Lea, 1862 accepted as Pleurocera canaliculata excurata (Conrad, 1834) accepted as Pleurocera canaliculata (Say, 1821) (junior synonym)
19. Species Io nodosa I. Lea, 1862 accepted as Pleurocera nobilis nodosa (I. Lea, 1862) accepted as Pleurocera nobilis (I. Lea, 1845) (original combination)
20. Species Io nolichuckyensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
21. Species Io pagodula (A. Gould, 1847) accepted as Brotia pagodula (A. Gould, 1847) (unaccepted combination)
22. Species Io paulensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
23. Species Io powellensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
24. Species Io recta Reeve, 1861 accepted as Io fluvialis (Say, 1825) (junior synonym)
25. Species Io rhombica Reeve, 1861 accepted as Io fluvialis (Say, 1825) (junior synonym)
26. Species Io robusta I. Lea, 1862 accepted as Pleurocera canaliculata undulata (Say, 1829) accepted as Pleurocera canaliculata (Say, 1821) (unaccepted > junior subjective synonym)
27. Species Io rota Reeve, 1860 accepted as Pachymelania aurita (O. F. Müller, 1774) (junior synonym)
28. Species Io spillmanii I. Lea, 1862 accepted as Pleurocera canaliculata excurata (Conrad, 1834) accepted as Pleurocera canaliculata (Say, 1821) (junior synonym)
29. Species Io spinosa I. Lea, 1834 accepted as Io fluvialis (Say, 1825) (junior synonym)
30. Species Io spirostoma J. G. Anthony, 1860 accepted as Io fluvialis (Say, 1825) (junior synonym)
31. Species Io tenebrosa I. Lea, 1841 accepted as Io fluvialis (Say, 1825) (junior synonym)
32. Species Io turrita J. G. Anthony, 1860 accepted as Io fluvialis (Say, 1825) (junior synonym)
33. Species Io unakensis C. C. Adams, 1915 accepted as Io fluvialis (Say, 1825) (junior synonym)
34. Species Io variabilis I. Lea, 1862 accepted as Pleurocera nobilis (I. Lea, 1845) (junior synonym)
35. Species Io verrucosa Reeve, 1860 accepted as Io fluvialis (Say, 1825) (junior synonym)
36. Species Io viridula I. Lea, 1862 accepted as Pleurocera prasinata (Conrad, 1834) (junior synonym; secondary homonym of Melania viridula Anthony, 1854; Pleurocera leaii Tryon, 1873 is a replacement name)
37. Species Io aenigmatica Bayan, 1870 † (uncertain > taxon inquirendum)
38. Species Io tuberculata A. Adams & H. Adams, 1858 (uncertain > nomen dubium)

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