Figs. 17, 46-47.
Etymology.- Latin "bifidus" ("split into two parts") +"clypeatus" ("provided with a shield")
Material examined.- Holotype: [[worker]], Prov. Antsiranana, rs Manongarivo 17.3 km 218 sw Antanambao 1580 m 14°01'3"s, 48°25'1"e, 160 m. 27.x.1998, b.l. Fisher 1972# /beating low vegetation montane rainforest/ 1972(05)-1 (cas). Paratypes: Prov. Antsiranana: (all specimens with same collection data as holotype): 1 [[worker]] (anic); 1 [[worker]] (bmnh); 1 [[queen]] (cas); 1 [[worker]] (mcz).
Other material examined: Prov. Antsiranana: r. s. Manongarivo, 17.3 km 218 sw Antanambao 27.x.1998 b.l. Fisher (1[[worker]]); r.s. Manongarivo, 20.4 km 219 swAntanambao 3.xi.1998 bl. Fisher (6 5). Prov. Fianarantsoa: 36 km s Ambalavao, Res Andringitra 29.x.1993 bl. Fisher (1 5).
Worker description.- Head: Head square, or rectangular; vertex planar or weakly concave; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter decumbent setae or setulae. Eye large, eye width 1.5x greater than greatest width of antennal scape, to moderate, eye width 1-1.5x greatest width of antennal scape; (in full-face view) eyes set at about midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; Antennal segments 12; antennal club three-segmented. Clypeal carinae always well-defined; anteromedian clypeal margin straight between strongly divergent clypeal carinae, clypeus descending almost vertically to arc of mandibles and sometimes transversely carinate below level of antennal insertions; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae, or, approximately level with antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes sinuate, divergent posteriad. Psammophore absent. Mandibular teeth three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, smooth (except for piliferous pits); masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).
Messoma: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; (viewed in profile) promesonotum broadly convex; promesonotal setae seven to twelve; standing promesonotal setae consisting of well-spaced, incurved, erect and semi-erect setae only; appressed promesonotal setulae few, mainly on sides of promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum shining and smooth, with a few weak striolae on metapleuron; propodeal dorsum convex; propodeum always smoothly rounded; standing propodeal setae consisting of one prominent pair anteriad, with other shorter setae very sparse or absent; appressed propodeal setulae very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle distinct in some specimens. Propodeal lobes present as rounded flanges, or, present as vestigial flanges or small strips of cuticle only.
Petiole and postpetiole: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex tapered, or, conical, vertex rounded; appearance of node shining and smooth throughout; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 3:4 and 2:3; anteroventral petiolar process present as a thin flange tapering posteriad, or, absent or vestigial; ventral petiolar lobe present; height ratio of petiole to postpetiole between 3:2 and 4:3; height -length ratio of postpetiole about 1:1; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial.
Gaster: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.
General characters: Color yellow to light brown, gaster often darker than head and mesosoma. Worker caste monomorphic.
Holotype: HML 1.22 HL 0.47 HW 0.42 CeI 88 SL 0.34 SI 82 PW 0.25.
Other worker measurements: HML 1.07-1.47 HL 0.43-0.55 HW 0.37-0.52 CeI 86-94 SL 0.32-0.44 SI 85-92 PW 0.21-0.29 (n=9).
Queen description.- Head: Head square; vertex weakly concave or planar; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter setae or setulae, which are decumbent or appressed, longer setae thickest on vertex. Eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin; (in full-face view) eyes set below midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule.
Mesosoma: Mesoscutum broadly convex anteriad, convexity reduced posteriad; pronotum, mesoscutum and mesopleuron shining and mainly smooth, vestigial striolae, if present, confined to anterior katepisternum; length-width ratio of mesoscutum and scutellum combined about 3:2; axillae separated by width of at least one axilla; standing pronotal/mesoscutal setae a mixture of wellspaced, distinctly longer, erect and semi-erect setae which are curved distally, interspersed with much shorter, incurved, decumbent setae; appressed pronotal, mescoscutal and mesopleural setulae few, mainly on sides of pronotum and mesopleuron. Propodeum shining and smooth, with a few distinct striolae on metapleuron; propodeum always smoothly rounded; propodeal dorsum convex; standing propodeal setae consisting of one pair of prominent setae anteriad, with a few smaller, erect to decumbent setae on and around dorsal and declivitous faces; appressed propodeal setulae very sparse or absent; propodeal spiracle nearer metanotal groove than declivitous face of propodeum; propodeal lobes present as vestigial flanges only, or absent.
Petiole and postpetiole: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex rounded; appearance of node shining and smooth; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1; anteroventral petiolar process present as a thin flange tapering posteriad; height ratio of petiole to postpetiole between 4:3 and 1:1; height-length ratio of postpetiole between 3:2 and 4:3; postpetiole shining, with vestigial sculpture; postpetiolar sternite without anterior lip or carina, or this structure vestigial.
Wing: Wing not seen (queen dealated).
Gaster: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.
General characters: Color yellow or yellowish-brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.
Queen measurements: HML 2.18 HL 0.61 HW 0.58 CeI 95 SL 0.48 SI 83 PW 0.44 (n=1).
Remarks.- This species appears to belong to a complex of very similar ants in which the head of the worker is relatively broad and the body is shiny and somewhat streamlined. Monomorium bifidoclypeatum has strongly defined clypeal carinae, and the anteromedian sector of the clypeus is depressed so that it forms an almost vertical, triangular plate. Seen in profile, the clypeal angle is approximately 90°. In other members of this complex, however, the clypeal carinae are poorly developed or obsolete, although the general conformation of the clypeus is the same. Monomorium bifidoclypeatum also has a distinct basal mandibular tooth, this anatomical feature being much reduced or even absent in the other species, except for M. chnodes . The sole known queen is rather similar in appearance to queens of M. termitobium (typical form). All but one of the specimens I have seen come from Antsiranana Province, where they were collected by beating low vegetation or by sifting litter from montane rainforest. One worker was collected as a forager in montane rainforest in Andringitra Reserve, Fianarantsoa Province.
