II. Key to subfamilies and tribes of North American terrestrial flatworms

The following key considers only the subfamilies and tribes of species that have been recorded in continental North America, as they are the most likely to be collected in the region. However, one should consider that terrestrial flatworms are regularly being introduced all over the world, therefore, a quick check of the rest of the taxa could prove beneficial while examining specimens. Histological characters, which can only be observed in transverse sections of prepared specimens, are given in brackets.

1 Head laterally expanded into a headplate, conspicuous (Fig. 27)..................................... BIPALIINAE

- Head narrow and inconspicuous (Fig. 28).................................................................. 2

2 Body subcylindrical, sometimes showing transverse striae in live specimens (Fig. 29); paired eyes at each side of the head (Fig. 30); [longitudinal cutaneous muscles arranged into a single layer, never in bundles] (Fig. 32)......... MICROPLANINAE

- Body flat or subcylindrical; eyes either paired (Fig. 30) or multiple (Fig. 31); [longitudinal cutaneous muscles arranged into bundles] (Fig. 33)..................................................................................... 3

3 Eyes numerous, arranged in two or more rows, some of which can extend to the dorsum; [testes located dorsally] (Fig. 34)............................................................................. GEOPLANINAE: Geoplanini

- With either paired eyes, or numerous eyes arranged in a single row which rarely extends to the dorsum; [testes located ventrally] (Fig. 35)....................................................................... RHYNCHODEMINAE: 4

4 Eyes paired, relatively large................................................................. Rhynchodemini

- Eyes multiple, arranged in a single row or clustering, often inconspicuous.............................. Caenoplanini