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Morphometric analyses of male genitalia are routinely used to distinguish genera and species in beetles, butterflies, and flies, but are rarely used in ants, where most morphometric analyses focus on the external morphology of the worker caste. In this work, we performed linear morphometric analysis of the male genitalia to distinguish Monomorium and Syllophopsis in Madagascar. For 80 specimens, we measured 10 morphometric characters, especially on the paramere, volsella, and penisvalvae. Three datasets were made from linear measurements: mean (raw data), the ratios of characters (ratio data), and the Removal of Allometric Variance (RAV data). The following quantitative methods were applied to these datasets: hierarchical clustering (Ward’s method), unconstrained ordination methods including Principal Component Analysis (PCA), Non-Metric Multidimensional Scaling analyses (NMDS), Linear Discriminant Analysis (LDA), and Conditional Inference Trees (CITs). The results from statistical analysis show that the ratios proved to be the most effective approach for genus-level differentiation. However, the RAV method exhibited overlap between the genera. Meanwhile, the raw data facilitated more nuanced distinctions at the species level compared with the ratios and RAV approaches. The CITs revealed that the ratios of denticle length of the valviceps (SeL) to the paramere height (PaH) effectively distinguished between genera and identified key variables for species-level differentiation. Overall, this study shows that linear morphometric analysis of male genitalia is a useful data source for taxonomic delimitation. 

The Camponotus subgenus Myrmosaga subgen. rev. from the Malagasy region is revised based on analysis of both qualitative morphological characters and morphometric traits. The multivariate analysis used the Nest Centroid (NC)-clustering method to generate species hypotheses based on 19 continuous morphological traits of minor workers. The proposed species hypotheses were confirmed by cumulative Linear Discriminant Analysis (LDA). Morphometric ratios for the subsets of minor and major workers were used in species descriptions and redefinitions. The present study places the subgenus Myrmopytia syn. nov. in synonymy to Myrmosaga . It recognizes 38 species, of which 19 are newly described: C. aina sp. nov. , C. aro sp. nov. , C. asara sp. nov. , C. atimo sp. nov. , C. bemaheva sp. nov. , C. bozaka sp. nov. , C. daraina sp. nov. , C. harenarum sp. nov. , C. joany sp. nov. , C. karsti sp. nov. , C. kelimaso sp. nov. , C. lokobe sp. nov. , C. mahafaly sp. nov. , C. niavo sp. nov. , C. rotrae sp. nov. , C. sambiranoensis sp. nov. , C. tapia sp. nov. , C. tendryi sp. nov. , C. vano sp. nov. Eleven species are redescribed: C. aurosus Roger, C. cervicalis Roger, C. dufouri Forel, C. gibber Forel, C. hagensii Forel, C. hova Forel, C. hovahovoides Forel, C. immaculatus Forel, C. quadrimaculatus Forel, C. roeseli Forel, C. strangulatus Santschi. The following are raised to species and redescribed: C. becki Santschi stat. nov. , C. boivini Forel stat. rev. , C. cemeryi Özdikmen stat. rev. , C. mixtellus Forel stat. nov. , C. radamae Forel stat. nov. Camponotus maculatus st. fairmairei Santschi syn. nov. , is synonymized under C. boivini . The following are synonymized under C. cervicalis : Camponotus cervicalis gaullei Santschi, syn. nov. ; Camponotus perroti Forel, syn. nov. ; Camponotus perroti aeschylus Forel, syn. nov. ; Camponotus gerberti Donisthorpe, syn. nov. Camponotus dufouri imerinensis Forel, syn. nov. is a synonym of C. dufouri , Camponotus hova var. obscuratus Emery, syn. nov. is a synonym of C. hova , Camponotus quadrimaculatus opacata Emery, syn. nov. is a synonym of C. immaculatus , Camponotus maculatus st. legionarium Santschi, syn. nov. is a synonym of C. roeseli , Camponotus hova maculatoides Emery, syn. nov. is a synonym of C. strangulatus . The following are synonymized under C. quadrimaculatus : Camponotus kelleri Forel, syn. nov. , Camponotus kelleri var. invalidus Forel, syn. nov. , Camponotus quadrimaculatus sellaris Emery, syn. nov. As C. imitator Forel, C. liandia Rakotonirina & Fisher, and C. lubbocki Forel have been recently described and redescribed, only diagnoses and taxonomic discussions are provided. This revision also includes an illustrated species identification key, taxonomic discussions, images, and distribution maps for each species superimposed on the ecoregions of Madagascar.