Following Vockeroth (1990), Carposcalis species (= stegnus group) have slender legs slender; profemur posteriorly with fine pile, ventrally at base sometimes with a few stiff setae; pro- and mesotibiae posteriorly on at least apical half with a single row of short and rather weak to long and strong black bristles; face slightly or moderately produced below, with pruinosity bearing distinct subshining punctures or oblique ripples or with pollinosity uniform except on tubercle; usually without keel between antennal bases; abdomen with paired subrectangular to subtriangular silvery to submetallic maculae on terga 2-4, the maculae sometimes with obscure or distinct dull orange background.
Platycheirus (Carposcalis) stegnus (Say, 1829).
Say, T. (1829-30) Descriptions of North American dipterous insects. Journal of the Academy of Natural Sciences of Philadelphia (1829) 6, 149-178 [1829.07.??], 183-188. [1830.08.??].
Say (1829) described stegnus as Syrphus. Enderlein (1938) described a new genus, Carposcalis, and designated Syrphus stegnus as the genotype. Vockeroth (1990) placed Carposcalis as a subgenus of Platycheirus.
Synonyms:
Syrphus stegnus Say, 1829: 163.
Melanostoma tigrina Osten Sacken, 1877: 323.
Platycheirus stegnoides Vockeroth, 1990: 738.
New description:
MALE.
Head: Face produced forward with facial tubercle, black, bluish silvery pollinose except lunule and medial broad shiny vitta, with pruinosity bearing distinct oblique ripples, black pilose; gena black, yellow pilose; lunule dark brown; frontal triangle black, bluish silvery pollinose; vertical triangle black, black pilose; antenna dark brown, basoflagellomere orange ventrally; occiput black, silver pollinose, withish-yellow pilose with black pili dorsally.
Thorax: Scutum and scutellum black with bluish silvery pollinose, black and yellow pilose; postpronotum bare; scutellar pili with wavy tips; subscutellar fringe complete with long yellow pile. Pleuron black, with bluish silvery pollinose, with long erected yellow pile except anterior anepisternum, posterior anepimeron and meron bare; metasternum bare; calypter yellowish white; plumula white; halter yellow; spiracular fringes yellowish. Wing: Wing membrane almost hyaline, microtrichose, except anterior half of cells CuP, BM and R bare. Alula broad, microtrichose. Legs: Coxae, trochanters and femora dark brown; apical 1/4 of the femora, tibiae and first three tarsomeres yellowish; 4th and 5th tarsomeres black. Protibia with about 11 slightly longer and weaker posterior bristles; bristles near tibial base very short. Mesotibia with about five long posterior bristles only slightly weaker than those of pro tibia. First tarsomere of metaleg less strongly swollen, about 4.5 times as long as greatest depth.
Abdomen: Parallel-sided. Dorsum mainly black, with a pair of dense shining silvery gray (submetallic) pollinose maculae on terga 2, 3 and 4; black pilose in black areas and yellow pilose mostly laterally and on pollinose maculae; 2nd tergum black with 2 medial silvery gray pollinose maculae broadly separated and broadening towards lateral margins; 3rd and 4th terga with 2 subbasal broad silvery gray pollinose maculae broadening towards lateral margins and posteriorly; 4th tergum with a medial silvery gray pollinose triangular maculae on posterior margin that may or may not reach anterior margin and join the two anterolateral amculae forming a fascia; 5th tergum mostly covered by dense shining silvery gray pollinosity.
unless otherwise stated