I have spent more time than I like to think about identifying bees of the genus Megachile, so I have no apology to make for offering somenotes which will, I hope, make the process easier for others:

Megachile frugalis, Cresson.— This species was described from the male. I have before me a female collected by Dr. Davidson at Lancester, California. It practically agrees with the description of M. zaptlana, Cresson, ♀, except that it has no lines of white pubescence on the thorax. M. occidentalis, Fox, ♀, is very similar, and has the lines of white pubescence, but it has a different clypeal margin, and the very scanty hair on the disc of the clypeus is white. In M. frugalis, ♀, the clypeus has long black hair; the ventral scopa is creamy white, black on the last segment. These bees are all of the elongate narrow type. The anterior margin of the clypeus in frugalis, ♀, can hardly be called excavated, but presents three gently-rounded prominences, the margin between them being slightly concave.