1.	Apical margin of clypeus strongly thickened	Osmia nigriventris (Zetterstedt)
–	Apical margin of clypeus more or less flat	2
2.	Propodeum shiny, propodeal triangle nearly completely polished or at least along sides with shiny area. Body length at least 11 mm [xanthomelana species group]	3
–	Propodeum and propodeal triangle completely shagreened and dull; body length at most 10 mm [inermis species group]	6
3.	T2 with impunctate apical margin medially rather broad (ca. length of F10); T4 polished (excluding the shagreened, impunctate apical margin)	4
–	T2 with impunctate apical margin narrower; T4 more or less shagreened throughout	5
4.	Integument with weak metallic sheen; mandible with rather weak, nearly absent, carina separating third tooth from second and fourth	Osmia pamirensis Gussakovskij
–	Integument lacking metallic sheen; mandible with relatively strong carina separating third tooth from second and fourth	Osmia maritima Friese, Osmia ephippiata Smith, and Osmia thoracica Radoszkowski [see Table 1 for further comments]
5.	Mandible with third tooth directed in same plane as second and fourth teeth, not set off from dorsal surface of mandible by carina; T2 with hairs medially on disc relatively long (ca. 640 micrometers), predominantly yellow-brown	Osmia xanthomelana (Kirby)
–	Mandible with third tooth directed slightly towards inner surface of mandible, set off from dorsal surface of mandible by carina extending from inner margins of second and fourth teeth; T2 with hairs medially on disc relatively short (ca. 400 micrometers), entirely black	Osmia alticola Benoist
6.	Declining basal portion of T1 densely shagreened, only with a silky luster	7
–	Declining basal portion of T1 shining, at most superficially shagreened in small areas	10
7.	Mandible with third tooth broad, not strongly separated from fourth tooth; forewing with veins cu-v and M intersecting vein M+Cu at the same place	8
–	Mandible with third tooth more triangular; forewing with cu-v intersecting vein M+Cu at a point distal to that of M	9
8.	Mandible on its inferior inner margin with prominent, asymmetrically triangular tooth; third tooth nearly filling entire space between second and fourth teeth; clypeus in profile only moderately convex	Osmia inermis (Zetterstedt) and Osmia ishikawai Hirashima
–	Mandible on its inferior inner margin nearly straight, without tooth; third tooth separated from second by indentation nearly one-third of entire space between second and fourth teeth; clypeus in profile strongly convex	Osmia disjuncta Tkalců
9.	Mandible with third tooth symmetrically triangular, broadly separated from both fourth and second teeth by acute-angled and broad indentation; mesepisternum with hairs predominantly blackish, only on its most anterior and uppermost part with narrow zone yellowish-brown; T2 with marginal zone not impressed, with punctures of disc basomedially finer, separated by up to three puncture diameters	Osmia svenssoni ­ Tkalců
–	Mandible with third tooth asymmetrically triangular, separated from second tooth by acute-angled and broad indentation, from fourth by shallow and rounded indentation; mesepisternum with hairs uniformly white to yellowish-white, sometimes with few intermixed blackish hairs; T2 with marginal zone impressed on its entire width, with punctures of disc basomedially coarser, separated by up to two puncture diameters	Osmia steinmanni Müller
10.	Distance between lateral ocellus and preoccipital margin two ocellar diameters; T2 and T3 with relatively well-defined, completely impunctate apical margin; integument with slight blue metallic sheen (especially on head and metasomal terga)	Osmia parietina Curtis
–	Distance between lateral ocellus and preoccipital margin three ocellar diameters; T2 and T3 with relatively broad apical margins with sparse, unevenly scattered punctures; integument lacking any metallic sheen	11
11.	Galea with short, completely straight hairs; mesepisternum with white to pale yellow hairs; T2 with hairs in the center of disc shorter (ca. 400 micrometers); T1 only with hairs strongly yellow-brown	12
–	Galea with much longer, incurved setae; mesepisternum with blackish hairs posteroventrally; T2 with hairs in the center of disc longer (ca. 560 micrometers); T1 and T2 with hairs strongly yellow-brown (T2 at the apical edge usually with weak admixture of black hair)	Osmia pilicornis Smith
12.	Clypeus in profile more convex, with punctures near base and in paraocular area relatively large and shallow (punctures basolaterally on clypeus distinctly larger than punctures basomedially on clypeus); forebasitarsal segment relatively long and thin (length ca. 3.5 times longer than width), length slightly longer than foretarsal segments two to five	Osmia uncinata Gerstäcker
–	Clypeus in profile less convex, with punctures near base and in paraocular area relatively small and deep (punctures basolaterally on clypeus the same size as those basomedially on clypeus); forebasitarsal segment relatively short and thick (length less than 3.0 times longer than width), length slightly shorter than foretarsal segments two to five	Osmia laticeps Thomson