Adapted from Vockeroth (1992).
MALE.
Head: Face strongly produced throughout, more than half as wide as head, with small subshining tubercle, otherwise lightly dark gray pollinose, with very faint median groove near upper end in some
specimens. Frontal triangle large, with dense rather long pie. Eyes meeting at an angle ofabout 110°. Antenna black with basoflagellomere orange ventrally.
Abdomen: Scutum and scutellum subshining, with long white or yellowish pile; longest scutellar pili slightly longer than arista. Pleura very slightly pollinose, with long white or yellowish pile. Wing extensively bare; cell c bare on basal one-third to three-quarters, cell bm bare except at apex and along about apical half of posterior margin. Halter capitulum yellow. Legs with coxae and trochanters black; profemur orange with blackish posterior vitta and with up to basal half of anterior surface black in some specimens; mesofemur orange with posterior surface narrowly black at base or with up to basal halfblack; metafemur usually black with about apical one-quarter orange but with orange-brown
vitta on entire posteroventral surface in some specimens; pro- and mesotibia orange with apical one-quarter slightly brownish in some specimens; metatibia orange at base becoming black toward apex; pro- and mesotarsus dark brown to black above with fifth tarsomere usually orange; metatarsus black. Profemur posteriorly with long fine dense mostly pale pili becoming slightly shorter toward apex and followed by two or three longer and stronger black pili with strongly curved apices, ventrally near base with row of three or four moderately strong straight yellow or black pile slightly longer than femoral
diameter; protibia posteriorly with many fine pale pile up to twice as long as tibial diameter; protarsus simple, with very short pile. Mesofemur anteroventrally with two irregular rows of strong stiff white or black pile; pili near base almost as long as femoral diameter, near apex appearing as short as fine setulae. Mesofemur posteroventrally near base with row of about four long strong black pili, posteriorly with long dense fine pile; mesotibia and tarsus with short pile. Metafemur anteriorly with long fine pile; metatibia with fine pale anterodorsal pile up to twice as long as tibial diameter; first tarsomere of metaleg moderately swollen, about 3.5 times as long as greatest depth.
Abdomen robust, with unusually long pile. Terga 2-4 with large subshining silvery gray pollinose maculae widely removed from lateral margins; maculae on tergum 2 near middle of sclerite; maculae on terga 3 and 4 reaching anterior margins; maculae of all terga usually with at least inner end and commonly with entire surface with dull orange background; tergum 5 black, subshining.
FEMALE.
Face with tubercle strongly shining, with pollinosity less uniform than in male. Frons shining with narrow pollinose margin on lower half; pollinosity extending triangularly inward at mid length so that from one-third to half of middle of frons shining. Thoracic pile shorter than in male but much longer than in related species. Cell c bare or microtrichose on at most apical one-third; cell bm with at most some microtrichia near apex. Femora and pro- and mesotibiae entirely orange; metatibia orange with up to apical half brown to black; tarsal color as in male. Abdomen broadly oval; markings similar to those of male but those of terga 3 and 4 and commonly those of terga 2 entirely bright orange and clearly defined; markings of tergum 2 subtriangular; markings of 3 and 4 subquadrate.
Snow (1895) described his kelloggi as Melanostoma. Wirth et al. (1965) included this species in the genus Carposcalis, but Vockeroth (1990) synonymized Carposcalis under Platycheirus.
Pachysphyria was a new genus that Enderlein (1938) described using Scaeva ambiguum Fallen, 1817 as genotype. Pachysphyria was considered synonym of Melanostoma by Wirth et al. (1965). Vockeroth (1990) included as Platycheirus almost all Nearctic Melanostoma. Thompson (2010) considered Pachysphyria as a subgenus of Platycheirus. There are several species in this subgenus: abruzzensis (Goot, 1969), coerulescens (Williston, 1887), dexter (Harris, 1780), fimbriatus (Loew, 1871), hirtipes (Kanervo, 1938), kelloggi (Snow, 1895), lundbecki (Collin, 1931), and transfugus (Zetterstedt, 1838).
Following Vockeroth notes (1990), Pachysphyria species have slender legs, with profemur usually with a row of stiff straight black setae posteriorly on at least apical half, the last seta longer and with apex strongly curved, in kelloggi only with dense fine pale pili and 2 or 3 weak curved black setae near apex.
Synonyms:
Melanostoma kelloggi Snow, 1895:230.
Melanostoma johnsoni Jones, 1917:220
Platycheirus (Pachysphyria) kelloggi (Snow, 1895).
Snow, W.A. (1895) Diptera of Colorado and New Mexico. Syrphidae. Kansas University Quarterly 3, 225-247.
unless otherwise stated