1	Tongue relatively short, extended length of glossum not reaching beyond mid length of metasoma (Figure 8a), second labial palpomere less than twice the length of the basal palpomere (Figures 3d and 3e)	2
–	Tongue long, extended length reaching almost to tip of metosoma (Figure 1), second labial palpomere at least three times the length of basal palpomere (Figures 3f and 3g)	3
2	Larger (13.5 mm), dark pubescence of T2 and T3 uniformly short and dense, maximum length less than half of width of pale apical fascia (Figure 9a)	Megachile chomskyi sp. n.
–	Smaller (≤11 mm), dark pubescence of T2 and T3 of intermixed length, length of longer, coarser dark hairs approaching width of apical fascia (Figure 9b)	Megachile amica Cresson
3	Larger (≥13 mm); pubescence on mesonotum entirely pale	Megachile umatillensis (Mitchell)
–	Smaller (11 mm); pubescence on mesoscutum and mesoscutellum with much black pubescence	Megachile oenotherae (Mitchell)