Neoathyreus

Neoathyreus (Mesoathyreus), new subgenus (Figs. 16–21)

Type species: Neoathyreus (Mesoathyreus) guyanensis, new species, here designated.

Size moderate, 11.0 to 15.0 mm in length. Sexually dimorphic; male (Figs. 16, 17) with distinct clypeal horn and elevated inner pronotal carinae; female (Figs. 18, 19) with trituberculate clypeus, median tubercle small, only slightly higher than lateral tubercles (typical for many Neoathyreus); pronotum with low, rounded inner and outer carinae. Characters similar in both sexes: right mandible trilobed, apical tooth broad, not narrowed into acute, slender tooth; left mandible bilobed, apical lobe lacking acute tooth, apex blunt. Labrum narrow, broadly emarginate, anterior edge briefly angulate or tuberculate medially. Clypeus with both anterior and posterior carinae extending onto median tubercle or horn. Vertex transversely concave in anterior half, surface punctate, punctures separated by about one diameter or more, most punctures each with small anterior tubercle; surface between obscurely, minutely granulate. Gena narrow, twice as wide or wider than anteriorposterior length, outer anterior angle rounded. Pronotal marginal bead unbroken, tubercle lacking medially on anterior margin; pronotal midline at least partially impressed; pronotal surface, except carinae and concavity in large males, punctate, many punctures each with small anterior tubercle with seta at base; lateral fovea on each side deep, almost circular. Scutellum small, narrow, at least twice as long as wide. Elytron lacking any trace of basal marginal bead; several slight irregularities near base only indication of striae; elytral disc punctate, not tuberculate, most punctures each with short, erect, pale seta; punctures usually separated by one diameter or less, surface between finely alutaceous, shiny. Foretibia with six teeth on outer margin, minute basal seventh tooth often present. Forecoxa closed, with small spine at outer posterior margin (similar to Neoathyreus). Metasternum slightly convex, midline represented by narrow, indented depression; anterior of metasternum rounded, very slightly angulate at anterior edge of midline. Hind tibia and tarsi resembling those of some Neoathyreus.

Remarks. While Mesoathyreus has a distinctive appearance, most of its characters can be found in one or more of the species of Neoathyreus. In establishing the genus Neoathyreus Howden and Martínez (1963) stated that “The genus could be further divided, but really distinct groups warranting even subgeneric status are not evident at this time”. While this is largely still true, Mesoathyreus has several characters that distinguish it and seems to warrant subgeneric status, at least until other groupings are established. The one consistent character that distinguishes both sexes of Mesoathyreus from species of Neoathyreus is the shape of the apical lobes of the mandibles, these being blunt in Mesoathyreus (Fig. 19); narrow, with an acute tip in Neoathyreus. The punctate, rather shiny dorsum, lack of elytral striae and the sexual dimorphism (only noticeable if both male majors and females are present) are characters that also may distinguish Mesoathyreus, but are not entirely unique, hence my proposal of a new subgenus rather than a genus.

Etymology. The subgeneric prefix “meso” = middle and is meant to indicate that Mesoathyreus should be placed between Athyreus and Neoathyreus. The name Mesoathyreus is masculine in gender.