The description is based on Vockeroth (1992) and on own findings.

Head: Eyes bare. Frontal triangle of male blackish, shining or with variable amount of dusting. Frons of female blackish, mostly shining with a pair of triangular dusted maculae above lunule. The size of these maculae varies and they are medially separated or confluent. Face and shallow facial tubercle blackish, shining or with a variable amount of dusting. Lunule black and shiny. Antenna varying from totally dark brown to largely yellow with brown dorsal margin of basoflagellomere.

Thorax: Scutum blackish, shining, usually with slight dusting anteriorly and laterally. Pili on scutum predominantly yellowish or whitish, rarely partly or totally blackish. Scutellum shining. Pleura mostly bare, blackish, shining or with variable amount of dusting. Katepimeron with widely separated dorsal and ventral pile patches. Metasternum consists of only a narrowly sclerotized anterior and median stripe. Wing: Usually totally microtrichose, at most with small bare areas around base of cell BM.

Legs: Coxa blackish. Metacoxa without posterior pile tuft. Femur, tibia and tarsus slender without outstanding pile or bristles. Coloration varies from almost totally yellow to almost totally dark brown.

Male abdomen: Nearly parallel sided, two to five times as long as greatest width. Terga 2–4 usually with sub-rectangular yellow maculae, but maculae sometimes darkened and/or reduced to various extent. Yellow maculae shining or with various amount of dusting. Maculae on tergum 2 separated from anterior margin. Maculae on terga 3–4 usually reaching anterior margins. Maculae on terga 2–4 usually reaching lateral margins and separated from posterior margins.

Female abdomen: Shape varying from nearly parallel sided to oval; two to four times as long as its greatest width. Terga 2–5 usually with yellow maculae but these maculae sometimes darkened and/or reduced to some extent. Maculae on tergum 2 roundish and separated from the margins. Terga 3–4 with anterior triangular maculae narrowly reaching lateral margins. Tergum 5 with or without anterolateral maculae.

FINLAND: Le: Enontekiö, Annjaloanji, [69°10'9"N, 21°25'22"E], ykj76865:2790.

Holotype: male, pinned, deposited in MZH. Original labels: ‘Finland, [69°10'9"N, 21°25'22"E], ykj76865:2790, Le: Enontekiö, Annjaloanji, 13.7.2007, A. Haarto leg. / DNA voucher specimen MZH_Y643, G. Ståhls, FMNH, Helsinki, Finland / Holotype Melanostoma certum Haarto & Ståhls 2013’. Paratypes: 1 male, FINLAND: EnL: Enontekiö Korkea Jehkas lampi, [69°4'39"N, 20°50'58"E], ykj76785:2553, 20.7.2005, K. Mattila leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [AHPC]; 1 male, FINLAND: Li: Utsjoki Pulmanki, [70°2'26"N, 27°53'53"E], ykj 77739:5344, 5.7.2004, J. Kahanpää leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [MZT]; 1 female, FINLAND: Li: Utsjoki, Karigasniemi, Ailigas, [69°24'51"N, 25°58'45"E], ykj77041:4601, 6.VII.2004, J. Kahanpää leg. / Melanostoma dubium A. Haarto det. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [MZH]; 1 female, FINLAND: Le: Enontekiö Annjaloanji, [69°10'9"N, 21°25'39"E], ykj76865:2790, 13.7.2007 (puro), A. Haarto leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [AHPC]; 1 female, FINLAND: Le: Enontekiö Jogasjärvi, [69°9'58"N, 21°27'50"E], ykj76860:2806, 11–16.7.2007, malaise, R. Jussila leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [MZT]; 1 female FINLAND: Le: Enontekiö Bumbovarri, [69°11'N 21 29'E], ykj7686:328, 9.7.2007, J.-P. Kaitila & M. Rantala leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [SKPC]; 1 female FINLAND: Le: Enontekiö Annjaloanji, [69°10'N, 21°26'E], ykj7686:328, 12.7.2007, J.-P. Kaitila & M. Rantala leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [SKPC]; 1 female FINLAND: Le: Enontekiö Toskaljoki, [69°10'34"N, 21°27'34"E], ykj76871:328, 12.7.2008, J.-P. Kaitila & M. Rantala leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [SKPC]; 1 male FINLAND: Le: Enontekiö Toskaljoki, [69°10'34''N, 21°27'34''E], 76871:328, 11.7.2008, J.-P. Kaitila & M. Rantala leg. / Paratype Melanostoma certum Haarto & Ståhls 2013’, [SKPC]; and six DNA voucher paratype specimens in MZH as listed in Table 1.

Head: Colour greyish black. Angle of approximation of eyes 85°–100°. Eye contiguity about as long as frontal triangle. Ocellar triangle slightly longer than wide with dark pile and indistinctly grey dusted. Occiput very narrow and usually with pale pile. Frontal triangle with indistinct or thin grey dusting. Lateral parts of frontal triangle with dark pile. Face shining with indistinct or thin grey dusting. Lateral parts of face with dark and pale pile. Gena about as wide as basoflagellomere and with greyish dusting. Antenna dark brown. Basoflagellomere about 1.3 times as long as wide. Arista brown and almost twice as long as basoflagellomere. Arista with extremely short pile, longest pile at the most half width of arista at base (Fig. 4B).

Thorax: Scutum shining greyish black except for thin greyish dusting at anterior margin. Scutum with erect whitish pile and with shorter semi-adpressed whitish pile on anterior margin. Anterior part of scutum with long erect pile which length at least third of length of scutellum. Postpronotum totally covered by thin greyish dusting. Notopleuron with thin greyish dusting. Scutellum shining greyish black, with whitish erect pile at its dorsum, hind margin and ventral side. Pleura greyish black with thin greyish dusting. Pleura with pale erect pile. Calypter brownish with pale brownish pile at edge. Halter yellow, with slightly darkened base of stem. Wing: Completely microtrichose, with slightly brownish ting. Stigma yellowish brown.

Legs: Coxa black with grey dusting. Trochanter dark brown. Femur usually mainly black except narrowly yellow apically. Tibia usually mainly dark brown except narrowly yellow bases and apices. Tarsus usually dark brown. Leg with pale and dark pile mixed.

Abdomen: Terga dark brown or black with dense or weak brownish dusting. Tergum 2 without or with pair of yellow roundish maculae. Terga 3 and 4 with pair of yellow subrectangular maculae. Terga 1 and 2 laterally with long whitish pile. Terga with pale and usually some dark semi-adpressed pile outside of yellow maculae. Only pale pile on yellow maculae. Terga 2, 3 and 4, each about 1.2 times as long as its width. Sterna weakly dusted and with pale semi-adpressed pile. Sternum 2 about 1.4 times as long as wide at its posterior margin. Sternum 3 about 1.3 times as long as wide at its anterior margin. Sternum 4 about 1.3 times as long as wide at its anterior margin. Shape of sterna 2–4 is shown in Fig. 5B. Male genitalia: Cercus and surstylus as in Fig. 6B. Postgonite short and without distinct ridges laterally (Figs 7B, 8B). Postgonite ventrally as in Fig. 9B. Margin of hypandrium near postgonites with short triangular projections, index DL more than 2.2 (Figs 10B, 11B).

Similar to male, but differs as follows:

Head: Frons shining except greyish dusted triangles which usually are medially confluent. Ventral to the dusted triangles the thinly dusted area is usually reaching the lateral area of lunule. Frons at level of front ocellus slightly narrower than length of antenna. Dorsal part of frons with dark pile and ventral part of frons with pale pile. Occiput as broad as two diameters of an ocellus and usually with pale pile.

Thorax: Scutum and scutellum with short pale pile. Calypter pale brownish with whitish pile at edge.

Legs: Coloration similar to male.

Abdomen: Terga 1 and 2 laterally with long whitish pile. Terga 2–5 dorsally with whitish semi-adpressed pile and always without yellow maculae. Terga 2 and 3 each about 0.5 times as long as wide at its posterior margin. Tergum 4 about 0.6 times as long as wide at its posterior margin. Sternum 2 about 0.6 times as long as wide at its posterior margin. Sternum 3 about 0.6 times as long as wide at its anterior margin. Sternum 4 at least 0.7 times as long as wide at its anterior margin. Sterna 3 and 4 almost parallel sided, rarely slightly broadened towards posterior margins. Shape of sterna 2–4 is shown in Fig. 12B, C.

(4 males and 6 females): Body 5–7 mm.

All verified specimens originate from North European localities north of 68°N, and almost all specimens are sampled at or above the tree line.

The word certum means clear, defined, and is to be treated as adjective in neutrum.

The locality of the lectotype is not indicated in the original label. Peck (1988) gave the following information “Auf Wiesen und in Wäldern nicht selten''“?Stolberg near Aachen''[Germany].

Lectotype of Melanostoma mellarium: female, pinned, deposited in MNHN. Original label: ’Meigen 1486 40 / mellinum type’. Here the lectotype is designated to fix the concept of Melanostoma mellarium (Meigen) and to ensure the universal and consistent interpretation of the same. Labelled: ‘LECTOTYPE Melanostoma mellarium (Meigen, 1822), Haarto & Ståhls des. 2013’. Images from MNHN.

of Melanostoma mellinum var. melanatus: female, pinned, deposited in MZT. Original label: ‘Haukilampi, 28.4.28'‘Lectotype Melanostoma mellinum var. melanatus Kanervo, Haarto & Ståhls des. 2014’.

DNA voucher specimens in MZH (Table 1) 17 males and 30 females in MZH; 25 male and 25 female specimens in AHPC.

Head: Colour black. Angle of approximation of eyes 80°–90°. Eye contiguity about as long as frontal triangle. Ocellar triangle slightly longer than wide with dark pile and with indistinct grey dusting. Occiput very narrow and dorsally with dark pile and laterally with pale pile. Frontal triangle shining with indistinct grey dusting. Lateral parts of frontal triangle with dark pile. Face shining with indistinct grey dusting. Lateral parts of face with pale and dark pile. Gena about as wide as basoflagellomere and with thin greyish dusting. Antenna mainly dark brown, basoflagellomere usually with a yellow spot baso-ventrally. Basoflagellomere about 1.3 times as long as its width. Arista usually brown and about twice as long as basoflagellomere. Longest pile of arista at most half width of arista at base as in Fig. 4B.

Thorax: Scutum shining black except for thin greyish dusting at anterior margin. Scutum usually with pale brown and dark erect pile and with shorter semi-adpressed pale pile on anterior margin. Pile rarely mainly dark on scutum. Anterior part of scutum with short erect pile which length about fourth part of length of scutellum. Postpronotum totally covered by thin greyish dusting. Notopleuron covered by indistinct greyish dusting. Scutellum shining black with pale and dark erect pile at its dorsum and posterior margin. Scutellum only pale pile at its ventral side. Pleura black and usually with only thin grey dusting and usually more distinctly shining on posterior part of anepisternum, anterior part of anepimeron and dorsal part of katepisternum. Pleura with pale erect pile. Calypter brownish with pale brownish pile on margin. Halter yellow with slightly darkened base of stem. Wing: Usually completely microtrichose, rarely with small bare area on base of cell BM. Membrane with slightly brownish ting. Stigma yellowish brown.

Legs: Coxa black with grey dusting. Trochanter dark brown. Femur usually mainly black except yellow apical part. Tibia usually mainly yellow with dark brown ring varying size. Metatibia usually with a longer dark ring than other tibiae. Tarsus dark brown except mesotarsus with two basal segments yellow. Leg with pale and dark pile mixed.

Abdomen: Terga dark brown or black with weak greyish dusting. Tergum 2 with pair of yellow oval maculae. Terga 3 and 4 with pair of yellow subrectangular maculae. Terga 1 and 2 laterally with long pale pile. Terga with varying amount of dark and pale semi-adpressed pile outside of yellow maculae. Only pale pile on yellow maculae. Terga 2, 3 and 4 each about 1.4 times as long as its width. Sterna with weak dusting and with pale semi-adpressed pile. Sternum 2 about 1.6 times as long as its width at its posterior margin. Sternum 3 about 1.5 times as long as its width at its anterior margin. Sternum 4 about 1.4 times as long as its width at its anterior margin. Shape of sterna 2–4 are shown in Fig. 5C. Male genitalia: Cercus and surstylus as in Fig. 6C. Postgonite long and with distinct ridges laterally (Figs 7C, 8C). Postgonite ventrally in Fig. 9C. The hypandrial, margin at postgonites with long triangular projections, index DL less than 1.2 (Figs 10C, 11C).

Similar to male, but differs as follows:

Head: Frons shining except greyish dusted triangles. Frons at level of front ocellus slightly narrower than length of antenna. Dorsal part of frons with dark pile and ventral part of frons with pale pile. Occipital orbit as broad as two diameters of an ocellus and usually dorsally with pale and dark pile and laterally with pale pile. Scape and pedicel brown or yellowish brown.

Thorax: Scutum and scutellum with short pale pile. Calypter whitish yellow with whitish pile at edge. Wing: Indistinctly brownish tinged. Stigma pale yellowish brown.

Legs: Femur and tibia usually mainly yellow with dark brown ring varying size. Metaleg usually largely darker than other leg.

Abdomen: Terga indistinctly grey dusted. Tergum 2 without or with a pair of small yellow oval maculae. Terga 3 and 4 usually with a pair of small yellow elongated triangular maculae. Tergum 5 at anterior margin without or with pair of short yellow maculae. Tergum 2 about 0.6 times as long as its width at its posterior margin. Tergum 3 about 0.7 times as long as its width at its posterior margin. Tergum 4 about 0.9 times as long as its width at its posterior margin. Sternum 2 about 0.8 times as long as its width at its posterior margin. Sternum 3 about 0.8 times as long as its width at its anterior margin. Sternum 4 about 0.8 times as long as its width at its anterior margin. Shape of sterna 2–4 are shown in Fig. 12D.

(25 males and 25 females): Body 7–9 mm.

We have verified specimens from Fennoscandia and central Europe, but data for a more detailed distributional map is presently not available.

The locality of the lectotype is not indicated in the original label. Peck (1988) gave the following information “Svecia'' (= Sweden).

Lectotype of Melanostoma mellinum: female, pinned, deposited in LSUK. We designate the specimen with collection number LINN 5304 as lectotype of Musca mellina Linnaeus, 1758. The lectotype bears no original label. Images: http://www.linnean-online.org/22691/.

Lectotype of Syrphus melliturgus: male, pinned, deposited in MNHN. Original label: ’Meigen 1482 40 / Syrphus melliturgus male’. Of the specimen only the thorax with legs and both wings remains. The identity of the specimen cannot be ascertained, but we accept the synonymy.

The type of Syrphus minutum Macquart, 1829 and syntypes of Syrphus unicolor Macquart, 1829 apparently exist at Musée d’Histoire Naturelle, Lille, France, but could not be studied.

Melanostoma mellinum var. melanatus (type material deposited in MZT) is here synonymized with Melanostoma mellarium.

The types of Melanostoma mellinum var. angustatoides Kanervo, 1934 are lost (see section Type studies).

The lectotype of Scaeva dubia Zetterstedt, 1838, original label ’S. dubia f Juckasjärvi'(in MZL) was studied, as well as one syntype (see section Type studies).

A male paratype of Melanostoma clausseni Barkalov, 2009 from the type locality (Russia, Altai, Ulaganskii region, Kuraiskii, 2500-2800m) was provided for study by A. V. Barkalov, and the taxon is here synonymized with Melanostoma mellinum. The type materials of remaining synonyms have not been studied.

DNA voucher specimens in MZH (Table 1); 85 males and 100 females in MZH; 25 male and 25 female specimens in AHPC.

Head: Colour brownish black. Angle of approximation of eyes 80°–90°. Eye contiguity about as long as frontal triangle. Ocellar triangle slightly longer than wide with dark pile and with thin grey dusting. Occiput very narrow and dorsally usually with dark pile and laterally with pale pile. Frontal triangle with indistinct or thin grey dusting. Lateral parts of frontal triangle with dark pile. Face shining with indistinct or thin grey dusting. Lateral parts of face with pile which colour varying from completely pale to almost completely dark. Gena about as wide as basoflagellomere and with greyish dusting. Antenna mainly dark brown, usually basoflagellomere with yellow spot basally at ventral side. Basoflagellomere about 1.4 times as long as its width. Arista usually yellowish brown and about twice as long as basoflagellomere. Longest pile of arista at most half width of arista at base as in Fig. 4B.

Thorax: Scutum shining brownish black except for thin greyish dusting at anterior margin. Scutum with erect pile and with shorter semi-adpressed usually mainly pale pile on anterior margin. Pile rarely mainly dark on scutum. Anterior part of scutum almost always with short erect pile which length about fourth part of length of scutellum. Postpronotum totally covered by thin greyish dusting. Notopleuron usually covered by thin greyish dusting. Scutellum shining brownish black. Scutum and scutellum with pile which colour varying from totally pale brown to almost totally dark. Pleura brownish black and usually with thinly grey dusting. Pleura with pale or brownish erect pile. Calypter brownish with pale brownish pile at edge. Halter yellow with slightly darkened base of stem.

Wing: Usually completely microtrichose, rarely with small bare area on base of cell BM. Membrane with indistinct brownish ting. Stigma usually yellowish brown.

Legs: Coxa black with grey dusting. Trochanter dark brown. Femur usually mainly black except yellow apical part. Tibia usually mainly yellow with dark brown ring varying size. Metatibia usually with a longer dark ring than other tibiae. Tarsus dark brown except mesotarsus with the two basal segments yellow. Leg with pale and dark pile mixed.

Abdomen: Terga dark brown or black with weak greyish dusting. Tergum 2 with pair of yellow oval maculae. Terga 3 and 4 with pair of yellow elongated maculae. Terga 1 and 2 laterally with long pale pile. Terga with varying amount of dark and pale semi-adpressed pile outside of yellow maculae. Only pale pile on yellow maculae. Terga 2, 3 and 4 each about as long as wide. Sterna with weak dusting and with pale semi-adpressed pile. Sternum 2 about 1.3 times as long as its width at its posterior margin. Sternum 3 about 1.2 times as long as its width at its anterior margin. Sternum 4 about as long as its width at its anterior margin. Shape of sterna 2–4 are shown in Fig. 5D.

Male genitalia: Cercus and surstylus (Fig. 6D). Postgonite short and without distinct ridges laterally (Figs 7D, 8D). Postgonite ventrally in Fig. 9D. The hypandrial margin at postgonites with long triangular projections, index DL less than 1.2 (Figs 10D, 11D).

Similar to male, but differs as follows:

Head: Frons shining except greyish dusted triangles. Ventral to the dusted triangles the thinly dusted area is not connected to the sides of lunule. Frons at level of front ocellus slightly narrower than length of antenna. Dorsal part of frons with dark pile and ventral part of frons with pale pile. Occiput as broad as two diameters of an ocellus and usually dorsally with pale and dark pile and laterally with pale pile.

Thorax: Scutum and scutellum with short pale pile. Calypter whitish yellow with whitish pile at edge.

Legs: Coloration of femur varies from mainly yellow to mainly dark. Metaleg usually largely darker than other leg.

Abdomen: Some specimens have all terga dorsally only with pale yellowish semi-adpressed pile. Tergum 2 without or with pair of small yellow oval maculae. Terga 3 and 4 with pair of yellow elongated triangular maculae of varying size or yellow maculae lacking. Tergum 5 at anterior margin without or with pair of short yellow maculae. Tergum 2 about 0.5 times as long as its width at its posterior margin. Tergum 3 about 0.5 times as long as its width at its posterior margin. Tergum 4 about 0.6 times as long as its width at its posterior margin. Sternum 2 about 0.6 times as long as its width at its posterior margin. Sternum 3 about 0.6 times as long as its width at its anterior margin. Sternum 4 about 0.6 times as long as its width at its anterior margin. Sterna 3 and 4 with posterior margin of sternum distinctly broader than width of anterior margin of sternum. Sternum 4 is at most slightly longer than sternum 3. Shape of sterna 2–4 are shown in Fig. 12E, F.

(25 males and 25 females): Body 6–8 mm.

A very common and abundant species, known from the whole Palaearctic area and North Africa.

Fabricius (1794) described this species from “Kiliae'' (= Kiel, Germany).

Types were not studied.

DNA voucher specimens in MZH from Hungary, Italy, the Netherlands and Finland (MZH); 16 male and 20 female specimens from Luxembourg, Netherlands, Serbia, Sweden (MZH); 25 male and 25 female specimens in AHPC.

Head: Colour bluish black. Angle of approximation of eyes 80°–90°. Eye contiguity about as long as length of frontal triangle. Ocellar triangle slightly longer than wide with dark and pale pile and with thin grey dusting. Occiput very narrow and with pale pile. Frontal triangle with dense grey or yellowish grey dusting except area above lunule with thin dusting. Lateral parts of frontal triangle with pale pile. Face with dense grey or yellowish grey dusting except shiny facial tubercle. Lateral parts of face with pale pile. Gena about as wide as basoflagellomere and with dense greyish dusting. Antenna mainly yellow, anterodorsal margin of basoflagellomere distinctly brown. Basoflagellomere about 1.5 times as long as wide. Arista yellowish brown and about twice as long as length of basoflagellomere. Arista short pubescent with pile about as long as width of base of arista (Fig. 4A).

Thorax: Scutum shining bluish black except for thin greyish dusting at anterior margin. Scutum with pale yellow erect pile and with shorter pale semi-adpressed pile on anterior margin. Anterior part of scutum with long erect pale pile which length at most third of length of scutellum. Postpronotum totally covered with dense greyish dusting. Notopleuron covered with greyish dusting. Scutellum shining bluish black with pale erect pile at its dorsum, hind margin and ventral side. Pleura bluish black with grey or yellowish grey dusting. Pleura with pale erect pile. Calypter whitish yellow with whitish pile at edge. Halter yellow with slightly darkened base of stem.

Wing: Microtrichose except for cell BM basally narrowly bare, with indistinct brownish ting. Stigma pale yellowish brown.

Legs: Coxa black with grey dusting. Trochanter yellowish brown. Femur and tibia yellow and brown in varying extent. Tarsus yellowish brown. Metaleg usually darker than other leg. Leg with all pile pale.

Abdomen: Terga dark brown or black with weak greyish dusting. Tergum 2 with yellow long oval maculae. Terga 3 and 4 with a pair of long yellow subrectangular maculae. Terga 1 and 2 laterally with long pale pile. Terga with dark and pale semi-adpressed pile. Pale pile on yellow maculae. Terga 2, 3 and 4 each about twice as long as wide. Sterna with weak dusting and with pale semi-adpressed pile. Sternum 2 about 2.5 times as long as its width at its posterior margin. Sternum 3 about twice as long as its width at its anterior margin. Sternum 4 nearly twice as long as its width at its anterior margin. Shape of sterna 2–4 are shown in Fig. 5A.

Male genitalia: Cercus and surstylus (Fig. 6A). Postgonite long and without distinct ridges laterally (Figs 7A, 8A). Postgonite ventrally in Fig. 9A. The hypandrial margin at postgonites with short triangular projections, index DL about 1.5 (Figs 10A, 11A).

Similar to male, but differs as follows:

Head: Frons shining except greyish dusted triangles which narrowly connected to dusted area of face. Frons at level of front ocellus about as broad as length of antenna. Occiput as broad as two diameters of an ocellus.

Thorax: Scutum with short pale pile.

Abdomen: Tergum 2 with pair of yellow oval maculae. Terga 3 and 4 with a pair of yellow elongated triangular maculae. Tergum 5 at anterior margin with a pair of short yellow maculae. Tergum 2 about 0.6 times as long as its width at its posterior margin. Tergum 3 about 0.7 times as long as its width at its posterior margin. Tergum 4 about 0.9 times as long as its width at its posterior margin. Sternum 2 about 0.8 times as long as its width at its posterior margin. Sternum 3 about 0.8 times as long as its width at its anterior margin. Sternum 4 about 0.9 times as long as its width at its anterior margin. Shape of sterna 2-4 are shown in Fig. 12A.

(25 males and 25 females): Body 7–9 mm.

A very common and abundant species, known from the whole Palaearctic area and Northern Africa.