Shannon described a new genus, Calostigma, for species with straight and upright vein M1 and the apical macula in the wing. These species are small, mostly polished flies with head hemispherical, circular in outline (frontal view), face projecting beyond antennal prominence; front unusually narrow; ocelli well advanced of occipital margin; eye nearly bordering onto oral margin; posterior oral region yellow; dorsum of thorax bounded by a yellow vitta; katatergum yellow; abdomen constricted basally; terga 3, 4 and 5 each with five longitudinal yellow vittae; post angular section of vein M1 straight and joining vein R4+5 at right angles; a conspicuous dark spot at tip of wing (Shannon 1927).
Calostigma was originally described as a genus by Shannon (1927), but Hull (1949) considered it as a subgenus of Baccha. Thompson et al. (1976) placed it under Ocyptamus.
Synonym:
Calostigma elnora Shannon, 1927: 9.
New description:
FEMALE.
Head: Face and front yellow, except for a black macula immediately above base of antennae and the ocellar region black; gena linear, yellow; antennae small, yellow, black pilose; eye bare. Occiput black, silvery pollinose (except the dorsal middle point), yellow pilose.
Thorax: scutum shining black with a broad yellow lateral vitta and with three medial white pollinose vittae, only hte medial vitta reaches the scutellum, yellow pilsoe laterally and black pilose medially; scutellum yellow with medial black macula, black pilose; subscutellar fringe incomplete, sparse with dark pile. Pleuron mostly yellow, except posterior anepisternum black on anterior half, katepisternum mostly black except dorsal yellow macula, and katatergum blak posteriorly; anepimeron with small dark maculae; anterior anepisternum pilose dorsally; metasternum bare; metaepimeron bare; calypter yellow; plumula absent; halter yellow; spiracular fringes yellow. Wing: Wing membrane mostly hyaline, except stigma dark and apical dark macula on cell R2+3; apically microtrichose, bare basally on cells Cup, BM, R and R1, and costal cell bare basally. Alula narrow, as wide as costal cell, bare. Legs: pro- and mesolegs entirely yellow; metaleg yellow, metafemur with brown subapical ring, metatibia dark with medial yellow ring; metatarsi yellowish, becoming darker apically.
Abdomen: unmargined, with second tergum constricted basally widening posteriorly; tergum 1 black, yellow laterally; tergum 2 black, yellow laterally, with medial yellow vittate macula and two submedial triangular yellow maculae joining posteriorly with the yellow lateral margin; terga 3, 4 and 5 black with medial yellow vitta, two submedial vittae and two sublateral vittae, which do not reach posterior margin in terga 3 and 4.
Ocyptamus (Calostigma) elnora (Shannon, 1927).
Shannon, R.C. (1927) A review of the South American two-winged flies of the family Syrphidae. Proceedings of the United States National Museum 70(9)[= No. 2658], 34 p. [1927.04.29]
unless otherwise stated