Ambiguity in the purported diagnostic attributes utilized to identify species of the poorly known “Troglopagurus group” of the hermit crab genus Diogenes prompted a review and critical reassessment of the morphological characters used to differentiate the nine recorded taxa. For this, an analysis was conducted based on 122 individuals including the majority of type specimens. The data clearly showed that the intraspecific variation inherent in these taxa rendered the presumably diagnostic characters ineffective in differentiating among the seemingly distinct species. As a result of the investigation, Diogenes setocristatus and Diogenes stenops were found to be junior subjective synonyms of Diogenes jousseaumei. Similarly, Diogenes platyops proved to be a junior subjective synonym of Diogenes jubatus. The incorrectly interpreted D. manaarensis was reappraised, based on the remaining syntype, herein designated the lectotype, and variations in the morphologies of the inadequately described D. persicus and D. mercatoris were explicated. Diogenes crosnieri has been retained as a valid taxon in the “Troglopagurus group”, at least until such time as more material becomes available.