The scorpion fauna of East Africa, encompassing Burundi, Kenya, Tanzania, Rwanda, and Uganda, is more diverse than those of West and Central Africa, but a systematic survey has never been conducted and the distributions of its species remain poorly understood. A recent opportunity to examine two extensive collections of East African, and predominantly Kenyan, scorpions and new material acquired by the author permitted a reassessment of the fauna of the region. The present contribution, the first of several emanating from this research, comprises two parts. The first part presents a redefinition and revision of the scorpionid genus Pandinoides Fet, 1997, with a redescription of the type species, Pandinoides cavimanus (Pocock, 1888), a revalidation and redescription of Pandinoides militaris (Pocock, 1900), and a description of Pandinoides duffmackayi, sp. nov. Pending reassessment of the genera and subgenera of Pandinus, sensu lato, based on quantitative phylogenetic analysis, Pandinoides is restricted to the three species with a marked concave depression in the retrodorsal surface of the pedipalp chela manus of the adult male, and Pandinus platycheles Werner, 1916, transferred to Pandinus subgenus Pandinoriens Rossi, 2015, creating a new combination: Pandinus (Pandinoriens) platycheles (Werner, 1916), comb. nov. The availability of large series comprising both sexes and all stages of the three Pandinoides species covered herein revealed considerable variation in counts of pedipalp trichobothria, spiniform macrosetae of the leg telotarsi, and pectinal teeth, among and even within individual conspecifics, calling into question the widespread practice of defining species and supraspecific taxa almost exclusively on trivial meristic differences between small samples of material (often singletons, female or immature). Furthermore, whereas neobothriotaxic patterns with low counts may provide appropriate diagnostic characters for genera and species, in combination with other characters, this is generally inadvisable when trichobothrial counts are high, due to the greater instability of the patterns.
The second part of this contribution assesses the validity of several putative species of Pandinus, sensu lato, recently described or revalidated, in light of data presented in the first part, and presents 10 new synonyms: Heterometrus roeseli Simon, 1872 = Pandinus (P.) imperator (C.L. Koch, 1841), syn. nov.; Pandinus (P.) camerounensis Lourenço, 2014 = Pandinus (P.) imperator (C.L. Koch, 1841), syn. nov.; Pandinurus (P.)