General view. Beetle large. Body slightly narrowed to apex. Pubescence very dense, appressed, nitidous (Fig. 1, 1). Head. Frons convex. Clypeus transverse, straight. Labrum bilobate. Eyes round, convex, without notches (Fig. 1, 2). Last segment of maxillary palpi is rhomboid (Fig. 1, 3). Antennae pectinate from the 4th segment; 1st segment is thick, slightly falciform; the 2nd one is very small, globose, transverse; 3rd segment is triangular, with concave apical margin (Fig. 1, 4). (8–11th (?) segments are lost). Pronotum with full side margin, transverse, convex, without gibbousness (Fig. 1, 5). Pronotal basal margin is as wide as elytral shoulders’ width. Disc with thin median line and triangular relief outlined by pubescence. Lateral margins not flattened. Basal margin is slightly arcuate. Sides convex, and pronotum narrows forward in a semicircle(Fig. 1, 1). Scutellum small, triangular. Elytra: shoulders well developed. Disc with four costae; 2nd, 3rd, and 4th costae merged in one, not reaching a little the apex. Sides with two lateral grooves and two lateral costae. Interstriae with large irregular punctures. Lateral margin without notch for the hind legs. Prosternum is very short, fore coxae approximated. Middle coxae a little separated. Metasternum convex, with median groove; meso- and metasternum united by thin carina (Fig. 1, 6). Anterior margin of metasternum without impressions for middle coxae. Epimera broaden forward. Hind coxae separated. Legs. Femora long. Middle tibiae and tarsi thin. Tarsi much more shorter than tibiae. First tarsus segment is very long (Fig. 1, 7). Abdomen. 1st sternite without impressions for hind legs and is the longest; 2nd sternite is a little shorter, then in decreasing order: 5th, 3rd, 4th sternites. First suture is single, slightly curved backward. The other sutures are straight and doubled.
We placed the new genus in the subfamily Ptilininae. Ptilinastidius slightly resembles the genus Phanerochila Fleutiaux, 1896: body narrows to apex, pronotum and elytra with costae, abdominal sternites of the same length and similar sutures. The new genus differs from Ptilinus Müller, 1764 and Ptilinomorphus Español, 1965 by narrowing body (body of cylindrical shape in the named genera); by the absence of teeth on pronotum (surface with teeth on pronotum in the named genera); eyes of average size (enormous eyes in Ptilinomorphus); by rhomboid maxillary palpus (fusiform maxillary palpus in Ptilinomorphus (Fig. 2, 4)); elytral surface with costae (elytral surface without costae in the named genera). Species of the genera Ptilinomorphus and Ptilinus are about twice as small as Ptilinastidius mirabilis.
Ptilinastidius strongly differs from the genus Ptilinobium White, 1976 by antennae (4–7th segments with rami in Ptilinastidius and without rami in Ptilinobium), pronotum (apical margin with group of long hairs in Ptilinobium whereas pronotal apical margin smooth in Ptilinastidius), elytra (elytral surface striate, without costae in Ptilinobium), abdomen (2nd sternite is the longest in Ptilinobium whereas 1st sternite is the longest in Ptilinastidius), members of each pair of middle and hind coxae are separated in Ptilinastidius whereas these members are touching in Ptilinobium.
P. mirabilis sp. n.
Beetle very dark brown; pubescence very dense, appressed, silvery, nitidous, absolutely covering the surface. Antennae reddish from the 4th segment. Body 2.7 times as long as wide (Fig. 1, 1). Frons convex, grumose. Eyes bulging, round, separated by 1.5 diameters of an eye (Fig. 1, 2). Last segment of maxillary palpus is rhomboid, 2.4 times as long as wide (Fig. 1, 3). Antennae: 1st segment large, thick, slightly falciform; the 2nd one is small, globose; 3rd segment triangular, rather large, with concave apical margin; 4th to 7th segments with rami. Ramus of 4th segment about 1.5 times as long as the segment itself, ramus of the 5th segment 2.5 times as long as the segment; rami of 6th and 7th segments 3 times as long as their segments (Fig. 1, 4). (Last segments are lost.) Pronotum 1.5 times as wide as long. Anterior angles slightly acute, rounded, posterior ones strongly rounded. Sides not flattened and not bulging (Fig. 1, 5). Disc with thin middle line and with triangular relief. Scutellum small, triangular, with obtuse top. Elytra twice as long as wide and three times as long as pronotum. Disc with four costae; every costa covered with silvery pubescence, which is directed obliquely to the middle of the costa. The first and second costae almost merged into the broad costa. Sides with two costae and two lateral punctured striae. Interstriae with large irregular punctures. Metasternum convex, with median groove; its anterior margin without impressions for the middle legs (Fig. 1, 6). Legs. Middle tarsi smaller than half of the tibia length (tarsus is 0.44 times as long as tibia). 1st tarsimere about as long as 2nd to 5th tarsimeres together (Fig. 1, 7). (Fore and hind legs are lost.) Length 10.8 mm, width 4.0 mm.