Key for the genera (mainly adult specimens)

1. Pedipalp chelae very robust (Fig. 2). Ventral surface of the pedipalp patella with three trichobothria (Fig. 3). Sternum clearly pentagonal (Fig. 4). Pectines with six to eight teeth (Fig. 4). Leg tarsomere II (telotarsus) with two rows of spine-like setae (Fig. 5). ........................( Diplocentridae) 2

– Pedipalp chelae feeble (Fig. 8). Ventral surface of the pedipalp patella without trichobothria. Sternum subtriangular to subpentagonal (Fig. 9). Pectines with more than eight teeth (Figs. 9, 12-14). Leg tarsomere II (telotarsus) without spine-like setae. .............. ( Buthidae) 3

2. Ventral surface of the metasomal segment V with a distal semicircular area, anteriorly delimited for well-defined transversal carina (Fig. 6). ................................... Cazierius

– Ventral surface of the metasomal segment V without a distal semicircular area, with the transversal carina poorly defined (Fig. 7). ............................................... Heteronebo

3. Pedipalp fixed finger with six rows of denticles, being the basal one very long (it occupies almost the basal one-half of the finger). ...................................................... Isometrus

– Pedipalp fixed finger with more than six rows of denticles, being the basal one very short (it occupies approximately one-eighth of the total length of the finger). ................... 4

4. Pedipalp fingers with inner accessory denticles and accessory outer denticles (Fig. 10). .................................. 5

– Pedipalp fingers without either inner accessory denticles or outer accessory denticles (Fig. 11). ................................. 6

5. Sternite III (the first post-pectinal) with a well-developed pair of longitudinal furrows, which converge towards the anterior part of the plate (Fig. 9). .................. Heteroctenus

– Sternite III (the first post-pectinal) without longitudinal furrows or a feebly submedian pair only. ..... Centruroides

6. Carapace subtriangular. Tergites with at least three welldeveloped longitudinal carinae. Pedipalp fingers with the median rows of denticles not imbricate. .......... Microtityus

– Carapace subrectangular. Tergites with a single longitudinal carina. Pedipalp fingers with the median rows of denticles clearly imbricate (Fig. 11). ........................................ Tityus