Taxonomy of ' Euconnus complex'. Part XXIV. Intermediate forms between Psomophus, Eupentarius and Euconnus s. str. in the East Palaearctic fauna unify problematic subgenera (Coleoptera, Staphylinidae, Scydmaeninae) Jałoszyński, Paweł Zootaxa 2022 2022-10-06 5194 3 343 391 8VRNT Thomson [763,887,432,458] Insecta Staphylinidae Euconnus Animalia Coleoptera 44 387 Arthropoda genus  The subgeneric division of  Euconnus, or even limits of the genus, are still problematic. The Malagasy  Madagassoconnusseems to be derived from the continental African  Tetramelus, and  Oneilamay only be a species group within  Tetramelus. The endemic New Caledonian  Austroconophronseems to be a good candidate to merge with  Euconnus s. str., as it does not have any peculiar characters to maintain it as a separate subgenus. New intermediate forms may be found and some of the existing subgenera may require merging into one. Some subgenera are defined mainly or exclusively by male dimorphic features and females cannot be placed to subgenus. Such subgenera may in fact represent species groups derived from within  Euconnus s. str.Moreover, some described species of  Euconnusnot placed to subgenus show a unique set of features that may justify proposing a new subgenus, e.g. a large group of Sri Lankan species including and similar to  E. mutabilis Franz, 1982. Such species in the key would very likely go to  Euconnus s. str.For these reasons, the key should be treated as a summary of the hitherto made changes in the classification of  Euconnus, pending further study. The same key with illustrated morphological structures is given in Figs 115–117. The key, already in its current form, has a serious flaw.  Euconnus kraatzi, previously placed in  Psomophus, and now in  Euconnus s. str., has the pronotum broadest clearly in front of middle. This species is not possible to place to subgenus using the key presented below, and there may be more similar  Euconnusspp.  Euconnus kraatziseems to be an intermediate form between  Euconnus s. str.and the subgenus  Tetramelus, and in future these subgenera may be merged. The European  Tetramelusspeciesare wingless, and consequently they have reduced humeral structures of the elytra. Their antennal clubs are either gradually thickened or with tetramerous clubs, and their pronotal structures and mouthparts are relatively diverse (e.g., Orousset 2015). Outside Europe, especially in Africa and Australia, there are species that are highly similar to the European  Tetramelusbut winged, and therefore the silhouette of their elytra is clearly different, because the humeral calli are strongly developed.  Tetramelusmay only be a group (or several unrelated groups) within  Euconnus s. str.This problem requires further study, preferably by molecular methods. Although I prefer in the present study not to go as far as merging  Tetrameluswith  Euconnus s. str.(even though there are firm morphological reasons), the fact that it was impossible to construct a key to subgenera that would not allow for exceptions (as  E. kraatzi) clearly demonstrates that the subgeneric system of  Euconnusis still impractical and very likely does not reflect phylogenetic relationships. It is presented nevertheless, as a starting point for future work. There is another reason to publish a ‘flawed’ key. Most of the problematic species, as  E. kraatzi, would be impossible to key out, and when such a case is encountered, it may mean that the species in question is particularly interesting. For instance, it may show some intermediate or unusual characters. Such species may in fact prove to be indispensable for further study of  Euconnus, one of the largest genera of any organisms on Earth. The key below can help identifying such interesting, problematic species, and this is one of its intended functions.     1 Hypostomal ridges running behind posterior submental margin as single transverse carina [ Madagascar].   NodoconnusFranz  - Hypostomal ridges running posteromesad................................................................. 2   2 Head ventrally with longitudinal gular groove; vertex with step-wise posterior narrowing (in some species indistinct) [Central and South America].................................................................   RhomboconnusFranz  - Gular groove lacking; vertex posteriorly not step-wise narrowed................................................ 3   3 Sides of pronotum with longitudinal hypomeral groove [ Madagascar]......................  GlabriconnusJałoszyński  - Hypomeral grooves lacking............................................................................. 4   4 Pronotum broadest in front of middle..................................................................... 5  - Pronotum broadest at middle, behind middle or with sides parallel in posterior half................................. 8   5 Antenna in male unmodified, gradually thickened or with variously distinct tetramerous club......................... 6  - Antenna in male modified.............................................................................. 7   6 Tarsomere 4 inall legs with long distoventral lobe [ Madagascar]...........................   MadagassoconnusFranz  - Tarsomere 4 lacking long distoventral lobe [worldwide]..................................   TetramelusMotschulsky    7 Maleantennomeres 8‒9 with longitudinal microserrate mesal ridges; pronotal base with 6 pits and median longitudinal carina [Palaearctic].........................................................................   CladoconnusReitter  - 1‒3 middle antennomeres in males enlarged and asymmetrical; pronotal base with 4 pits and lacking median carina [ South Africa] ................................................................................   OneilaPeringuey   8 Antennal club in males trimerous AND distinctly modified, with at least antennomere 9 asymmetrical [Borneo].............................................................................................   BorneoconnusFranz  - Antennal club in males either not trimerous, or, if clearly trimerous, lacking asymmetrically modified antennomeres...... 9   9 In males, antennae gradually thickened and antennomeres 9‒11 (in some species 9 indistinctly) modified, with asymmetrical impressions and projections [Central and South America].....................................   AndroconnusFranz  - In males, antennae either with clearly delimited club or gradually thickeningAND antennomeres 10 and 11 lacking asymmetrical modifications....................................................................................... 10   10 Pronotum broadest at middle and similarly narrowing posterad and anterad, lacking any antebasal structures AND antennae in both sexes gradually thickening [ New Caledonia].......   AustroconophronFranz[possibly identical with  Euconnus s. str.]  - Pronotum of various shapes, but rarely as above, if equally narrowing anterad and posterad and lacking antebasal pits, grooves and carinae, then antenna with club [worldwide]...............................................   Euconnus s. str.