1. Species Isthmia enervis Ehrenberg, 1838
2. Species Isthmia inermis Ehrenberg
3. Species Isthmia nervosa Kützing, 1844
4. Species Isthmia squinaboli (Forti) Forti
5. Species Isthmia szaboi Pantocsek
6. Species Isthmia africana Ehrenberg, 1844 (uncertain > unassessed)
7. Species Isthmia capensis Grunow in Schmidt et al., 1888 (uncertain > unassessed)
8. Species Isthmia catenata Meneghini (uncertain > unassessed)
9. Species Isthmia domuslaterariae Reinhold, 1937 (uncertain > unassessed)
10. Species Isthmia filiformis (Ehrenberg) Meneghini (uncertain > unassessed)
11. Species Isthmia fortii Forti & Schulz, 1932 (uncertain > unassessed)
12. Species Isthmia japonica (Castracane) Sournia, 1968 accepted as Isthmia enervis var. japonica Castracane, 1886 (uncertain > unassessed)
13. Species Isthmia lindigiana Grunow & Eulenstein in Grunow, 1867 (uncertain > unassessed)
14. Species Isthmia membranacea Cleve, 1891 (uncertain > unassessed)
15. Species Isthmia minima Harvey & Bailey, 1862 (uncertain > unassessed)
16. Species Isthmia obliquata (J.E.Smith) C.Agardh, 1832 accepted as Diatoma obliquatum Lyngbye, 1819 (uncertain > unassessed)
17. Species Isthmia polymorpha Montagne, 1840 (uncertain > unassessed)
18. Species Isthmia reticularis Brun, 1896 (uncertain > unassessed)
19. Species Isthmia stomatophora (Turpin) Meneghini (uncertain > unassessed)
20. Species Isthmia tenuicornis Grunow, 1889 (uncertain > unassessed)
21. Species Isthmia vertebrata (Brébisson) Meneghini (uncertain > unassessed)
22. Species Isthmia vesiculosa (Agardh) Agardh, 1832 accepted as Diatoma vesiculosum Agardh, 1824 (uncertain > unassessed)
23. Species Isthmia vitrea Kitton, 1873 (uncertain > unassessed)

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