Key to species of Tribonium known from Argentina

1 L2’ with apophysis (ap) elongated and notoriously curved (Fig. 28)............................................. 2

- L2’ with apophysis (ap) straight......................................................................... 3

2 L3’: internal margin of apical hook almost straight (Fig. 26), subapical notch (45 in Fig. 36) is broad..................................................................................................... Tribonium neospectrum

- L3’: internal margin of apical hook convex; subapical notch narrow (Fig. 31 in Lopes, 1978)........ Tribonium spectrum

3 Caudal process of L2’ (via) (Figs. 8–9, 31) with cranial and caudal swellings (sw) ............... Tribonium rothi sp . n.

- Caudal process of L2’ (via) without swellings (Figs. 19, 32)................................................... 4

4 L3’ with a wide, sub-conical base that abruptly turns into a narrow neck (nk), its width is approximately 1/3 of its base’s diam- eter (Figs. 17, 35). The internal margin of the apical hook is smoothly convex, and its external curvature almost regular....................................................................................... Tribonium conspersum

- L3’ with a wide sub-conical base that abruptly turns into a broad neck (nk), its width is larger than half of the base’s diameter. The internal margin of the apical hook is scarcely convex, and its external curvature irregular (Fig. 36 in Lopes 1978)........................................................................................ Tribonium guttulosum