• Isthmolithus G. Deflandre, 1954 †
• Isthmolithus claviformis Brönnimann & Stradner, 1960 † accepted as Zygrhablithus bijugatus (G.V. Deflandre in G.V. Deflandre & Fert, 1954) G.V. Deflandre, 1959 †
• Isthmolithus recurvus Deflandre, 1954 †
• Isthmolithus rhenanus Martini, 1973 †
• Isthmolithus triplus Levin & Joerger, 1967 †
• Isthmolithus unipons Bramlette & Sullivan, 1961 †