Type species: D. assmuthi Wasmann, 1904.
Discoxenus Wasmann, 1904: 655; Seevers 1957: 264; Kistner, 1982: 165.
Diagnosis. This genus is distinguished from other genera in Compactopediina by a combination of following characters (states): body shape limuloid with abdomen gradually narrowed posteriorly, head completely covered by pronotum, antennae fusiform, antennal segment II small, petioles completely covered with antennal segments III– X, maxillary basistipes fused with palpifer partly or completely, tarsal formula 4 - 4-5.
Redescription. Body glossy, overall orange brown, antennae and elytra slightly darker (Figs. 1–18, 165, 166). Head capsule (Figs. 19, 38, 54, 73, 89, 105, 121, 137, 149) transverse, widest at eyes, sparsely covered with minute pores, completely covered by pronotum in dorsal view, several setae present at postgenae and anterior margin of clypeus; antennal shelf well developed, formed by anteriorly produced epicranium and clypeus, covered with several setae and pores; occipital suture absent. Eyes well developed. Gula short, strongly dilated posteriorly, fused to submentum. Antennae (Figs. 20, 39, 55, 74, 90, 106, 122, 138, 150) with 11 segments, fusiform except for segments I and II, widest at segment IV or V; apical margin of each segment fimbriated; segment I long, almost as long as segment XI, with 2 macrosetae; segment II short, narrower than other segments; pedicles invisible externally between segments III–X. Labrum (Figs. 21, 40, 56, 75, 91, 107, 123, 139, 151, left side) transverse, sparsely covered with pseudopores, with anterior margin concave at middle, 2–4 pairs of large primary setae present on anterior half, a pair of setaceous sensillae and minute sensillae present at middle of anterior margin (probably homologous to a - and b -sensillae of Sawada [1972]). Epipharynx (Figs. 21, 40, 56, 75, 91, 107, 123, 139, 151, right side) medially covered with few pores. Mandibles (Figs. 22, 23, 41, 42, 57, 58, 76, 77, 92, 93, 108, 109, 124, 125, 140, 141, 152, 153) asymmetric. Right mandibles with a small tooth. Maxilla (Figs. 24, 59) with medial sclerite of stipes (basistipes) somewhat fused with outer sclerite of stipes (palpifer), 2 long setae present at base of basistipes; palpus with 5 segments, segments II and III sparsely covered with setae and pores; lacinia with 10 thick setae apically; galea with 4–5 thick and long setae apically. Mentum (Figs. 25, 43, 60, 78, 94, 110, 126, 142, 154) distinct from submentum, with anterior margin submembranous, difficult to discriminate from membrane connected to labium, with lateral margin rounded, 2 pairs of long setae and a pair of short setae present at anterolateral corners. Prementum (Figs. 26, 61) with a pair of distal setae at anterior margin, a pair of setal pores present on posteromedial area; palpus with 4 segments; segment I with 2–3 setae; segment II with 5 setae on anterior half, aboral one seta longer than other setae.
Pronotum (Figs. 27, 44, 62, 79, 95, 111, 127, 143, 155) semicircular, dorsally convex, sparsely covered with minute pores. Elytron (Figs. 28, 45, 63, 80, 96, 112, 128, 144, 156) with posterior margin subtransparent, 4 long macrosetae present at outer lateral margin. Prosternum short, carinate at middle. Wings fully developed. Mesoventrite (Figs. 29, 64) medially covered with short setae, approximately half as long as metaventrite; mesoventral intercoxal process narrow, acutely developed posteriorly, fused with metaventral process. Metaventrite (Figs. 29, 64) sparsely covered with yellow setae and pores except for mesocoxal cavities, 2 pairs of macrosetae present at middle except for D. cambodiensis without macrosetae. Mesocoxal cavity completely margined. Legs short and flat, sparsely covered with setae. Fore coxa with a macroseta around apex; tibia with inner margin densely covered with setae, with 2–5 thick setae and 2 spurs at apex. Mid trochanter with a macroseta at middle; femur with 1–2 macrosetae at base and apex; tibia with apical half of inner margin densely covered with setae, 2–3 macrosetae present at outer margin, with 2–5 thick setae and 2 spurs at apex. Hind coxa with 1–2 macrosetae around inner margin; trochanter with a macrosetae at middle; femur with 1–2 macrosetae at base and apex; tibia with 2–3 macrosetae at outer margin, 2–6 thick setae and 2–3 spurs present at apex; tarsal segment I densely covered with yellow setae on inner margin. Tarsal formula 4 - 4-5.
Abdomen (Figs. 1–18) narrowed posteriorly. Sternites sparsely covered with yellow setae and macrosetae. Tergite IX (Figs. 33, 49, 68, 84, 100, 116, 132, 147, 160) fully subdivided by tergite X, with 5 pairs of macrosetae on posterior half. Tergite X with 3 pairs of macrosetae around posterior margin. Macrochaetotaxy varied in species.
Male. Median lobe of aedeagus (Figs. 34, 35, 50, 51, 69, 70, 85, 86, 101, 102, 117, 118, 133, 134, 161, 162) with basal capsule longer or as well as apical lobe; distal crest distinct, strongly developed in the assmuthi species group; copulatory piece long, longer or as long as apical lobe. Paramere (Figs. 36, 52, 71, 87, 103, 119, 135, 163) with paramerite covered with several pores at middle; condylite narrow, distinct from paramerite, covered with pores basally; velar sac sclerite (inner surface of paramerite) with 3–6 setae; apical lobe approximately on third as long as paramerite, sparsely covered with pores, several minute setae present.
Comments. Morphological characters of small body parts such as mouthparts are important features in Aleocharinae systematics (Sawada 1972). In this paper, we describe such characters observed in all the Cambodian species under study.