Genus Trirachys Hope

Trirachys Hope, 1841, Proc. Ent. Soc. Lond., : 61 (type-species : T. orientalis H.) loc. cit. - Aurivillius, 1912, Coleopt. Cat., 39 : 47. - Gressitt, 1940, Philip. J. Sci., 72 (1-2) : 43 - 44; 1951c, Longicornia 2 : 138. - Gressitt & Rondon, 1970, Pac. Ins. Monogr, 24: 66.

Diagnostic characters : frons with a diamond-shaped raised area; vertex with a ridge between upper eye lobe; antennal segment 5 - 7 spined endoapically in male, 5 - 10 in female; fore coxal cavity rounded; elytra densely pubescent, producing a changable patterns depending on angle of vision.

Key to species of Trirachys in Sarawak

1.   Prothorax transversely corrugated, ridges interrupted on each side of median; fore intercoxal process with bifurcate groove running along margin of coxae; apical margin of femora with two sharp processes; antennae 2 X as long as body in male, 1/4 longer in female; scape punctulate .............…2
Prothorax rugous-vermiculate, with a median flat area; bifurcate groove absent on fore intercoxal process; apical margin of femora rounded; antennae 1.5 X as long as body in male, slightly longer in female; scape subrugose and punctulate; antennal segment 5 - 10 distinctively spined endoapically in both sexes - sphaericothorax GRESSITT & RONDON, 1970

2(1) Endoapical spine on antennal segment 5 - 9 very distinctive; pronotum with two longitudinal groove - aurifaber WHITE
Antennal segment 5 - 7 briefly spined endoapically, spine on segment 8 - 9 barely visible; two longitudinal groove on pronotum less distinctive; last antennal segment twice as long as segment 10 in male - bilobulartus GRESSITT & RONDON, 1970

Trirachys sphaericothorax GRESSITT & RONDON

Trirachys sphaericothoras Gressitt & Rondon, 1970, Pac. Ins, Monogr., 24 : 69, fig. 13.g. (Houay Say : Bishop Museum)

Body pitchy with reddish tinge, very pubescent; mandible, frons, head and thorax black with numerous golden pubescence, denser in depressed areas; antennae black, brownish towards apex, sparsely pubescent; gula and ventral of thorax with dense golden bristles especially at margin; elytra pitchy, densely covered with golden pubescence lying in different direction giving a interchanging patterns; undersurfaces very pubescent; tibiae and femora sparsely covered with golden pubescence.

Head exerted, mandible acutely bent at apex, with a strong ridge running in the middle; anterior margin of clypeus forming a horizontal ridge with labrum, slightly extended over the labrum in male; frontal diamond-shaped area sunken; gula with a deep aduncate and impunctuate groove, elevated surface between eye lobe flat; two deep off median sulci in between antennal insertion, forming a impunctate ridge that end abruptly into a fovea just before posterior margin of upper eye lobe; neck with a weak median sulcus. Antenna 1.5 X longer than body in , slightly longer in ; scape subrugose and punctulate; segment 3 - 5 thicken apically in , only slightly thicken in ; segment 3 as long as 1 + 2 united in both sexes; segment 6 slightly longer than 3 and the remaining subequal; endoapical spine on segment 5 - 10 more distinctive in ; segment 6 - 10 of dentate ectoapically. Prothorax as wide as long, broadest at middle and as wide as elytra; side rounded, strongly convex; anterior and posterior end with a sinuate but complete transverse groove; pronotum with a median squarish raised flat surface, in front with a median oblong knob preceeded by two partially joint knob; side of pronotum strongly rugous­vermiculate, raised above basal and apical. constriction. Elytron 4 X as long as broad; gradually rounded at apex; dehiscent from middle onwards; truncate with sharp sutural spine and dentate subapically. Legs : femora compressed laterally, apical margin rounded; first hind tarsal segment as long as 2 + 3 united.

Measurement: Length 26.0 - 37.0 mm () ; 27.0 - 34.0 mm ()
Breadth 7.0 - 10.0 mm () ; 6.5 - 9.0 mm ()

Distribution: Loas ; Sarawak

Known habitat: secondary forest

Note : differ from orientalis Hope in the absent of lateral spine on prothorax and shorter antennae.

Material examined: 8 [424], Kampung Teh, Mukah, Sibu Div., Sarawak., 3.VI.1995, Meekiong Kalu. (UNIMAS Coll.); Santubond, Kuching Div., date unknown (SM Coll.); Sadond, Samarahan Div., IX.1903 (SM Coll.); Bidi, Bau, Kuching Div., VIII.1898 (SM Coll.); Samarahan, Samarahan Div., VI.1910 (SM Coll.); Sarawak, III.1896 (SM Coll.); Sadong, Samarahan Div., XI.1902 (SM Coll.); Buntal, Kuching Div., date unknown (SM Coll.); 5 [406], Serian, Kuching Div., Sarawak., 6.V.1995, Wahap Marni. (UNIMAS Coll.); Kuching, Kuching Div., VIII.1897 (SM Coll.); Sadong, Samarahan Div., IX.1903 (SM Coll.); Saribas, Sri Aman Div., 1900 (SM Coll.); [Y81-0182] Niah Res. Sta., Miri Div., 28.V.1980, Alex. & Yeo (For. Dept. Coll.).

Trirachys aurifaber WHITE

Trirachys aurifaber White (loc. cit)

Body pitchy, entire head including mandible black with tawny pubescence; scape fuscous, remaining segments pitchy with sparse but even tawny pubescence; prothorax pubescent throughout except longitudinal grooves; elytra densely covered with tawny pubescence, arranging in different direction producing variable slivery patterns; undersurfaces with dense tawny pubescence; legs sparsely pubescent.

Head much narrower than prothorax; fronts oblique; anterior margin of clypeus sinuate, finely puncture with several (4 - 9) coarse puncture near frontal fovea; diamond-shaped area elevated, at same level as frontal plane, surrounded by two foveae at side; middle ridge distinctively behind antennal insertion and terminate at a depression before posterior margin of upper eye lobe; gula with subsinuate groove, surface between lower eye lobe concave and coarsely puncture at side. Antenna 1.5 X longer than body in , 1/4 longer in ; scape cylindrical, densely and finely puncture; segment 3 & 4 thincken apically, beginning from middle in ; endoapical spine on segment 5 - 9 very distinctive in both sexes; 5 very much shorter than 3 in , slightly shorter in ; segment 6 - 10 with ectoapical cusp, less so in ; last segment 1.5 X longer than segment 10 in , same length in . Prothorax as long as wide; side parallel, a little narrow in front; pronotum transverse corrugated at basal half, subtransverse wrinkles at apical half, uniformly interrupted at both side of median producing two distinct, smooth and impunctate longitudinal grooves; prosternum with two transverse groove, many faint carinae behind the posterior one. Elytron 4.5 X as long as broad; disc flat, convex sideway; rounded towards apex; apex obliquely truncated, slightly emarginate with a sutural spine further inward than the pointed angular spine. Legs : femora compressed laterally, apical margin with two sharp pointing processes; first hind tarsal segment a little longer than 2 + 3 united.

Measurement: Length 32.0 - 47.0 mm (); 32.0 - 42.0 mm ()
Breadth 9.2 - 13.0 mm (); 8.0 - 11.5 mm ()

Distribution: Sarawak

Material examined : 6 [376], Sampling log pond, Tubau, Bintulu Div., 28.II.1995, C. L. Voon. (UNIMAS Coll.); Kuching, Kuching Div., 16.IV.1900 (SM Coll.); Kuching, Kuching Div., 29.IV.1899 (SM Coll.); Jegora, date unknown (SM Coll.); Kuching, Kuching Div., 1895 (SM Coll.); Limbang, Limbang Div., date unknown, Ward coll. (SM Coll.); 6 [B2], UPM campus, Bintulu Div., 8.II.1992, student. (UNIMAS Coll.); [FN 85-0394], Bukit Semalang, Belaga, Kapit Div., 8.IV.1985, Lippa Akeng. (For. Dept. Coll.); Kuching, Kuching Div., 7.III.1900 (SM Coll.); Limbang, Limbang Div., date unknown, Ward coll. (SM Coll.); Sarawak, date unknown (SM Coll.); Kuching, Kuching Div., 1891.

Trirachys bilobulartus GRESSITT & RONDON

Body dull fuscous with tawny pubescence on head and thorax; compressed side of antennal segment covered with dense but minute tawny pubescence; silvery pubescence on elytra arranged in different direction resulting a highly changable glistening patterns; undersurfaces densely and evenly covered with silvery pubescence.

Head exerted, gena margin and mandible almost parallel; anterior margin of clypeus transverse, notched at base of mandible and same plane as labrum; a depression at posterior margin of upper eye lobe preceded by a strong median ridge, the anterior portion being weaker and bound by two much stronger ridges between antennal insertion; gula with a horizontal groove, surface between eye lobe with a wide concave depression, finely puncture; neck finely granulose. Antenna 2 X as long as body in ; scape slightly thicken at apex; 3 & 4 abrubtly thicken at apical half, 5 subequal to 3; 6 - 11 strongly compressed laterally; 6 - 10 subequal; 11 longest, 2 X as long as segment 10; 5 - 7 briefly toothed endoapically, spine on 8 & 9 barely visible; 6 - 10 also dentate ectoapically. Prothorax a little longer than broad, much narrower at apex than at base; side slightly convex; apical margin thicken as if a ring around the neck, base sinuate; pronotum transversely corrugated, interrupted on side of median; margin of intercoxal process thicken along coxae leaving a bifurcate groove. Elytron 4.5 X as long as broad; disc convex; gradually narrow at 4/5 from base; subtransversely truncated with a suteral spine and angular tooth, both at the same level. Undersurfaces minutely puncture and densely pubescent. Legs : femora and tibiae compressed laterally; apical margin of mid and hind femora with two sharp pointing process.

Measurement : Length 37.0 mm (); breadth 10.4 mm ().

Distribution : Thailand; Laos; Sarawak.

Known habitat : logged over mixed dipterocarp forest (logging track)

Note : differ from aurifaber White in having less distinctive longitudinal goove on pronotum; antennal segment 5 - 7 briefly spined endoapically while spine on segment 8 - 9 barely visible; compressed side of antennal antennae densely covered with pubescence; elytra being more slivery.

Material examined : 1 [073], Sungai Tegulang, Kapit Div., Sarawak., 5.XII.1994, Wahap Marni. (UNIMAS Coll.).