It certainly wasn't very tiny!

but isn't it a Zacosmia? Xeromelecta is not very tiny.

at any rate I wouldn't label it "Xeromelecta...". On the other hand, enlarging the photo I think the marginal cell appears longer than stigma, or?
Re. length of bee, I'm thinking more along 8-10 mm based on the approximate length of petals. Yet, flagellum is clearly thickened so I might just misread the photo in terms of marginal cell?

Problem with sizing is that the Common Stork's Bills' flowers around this part of metropolitan Phoenix (north western suburb around 25-30 miles from downtown) have been smaller than usual this past year, certainly not with petals in the 10mm length range. The rainfall has been much less than normal for two, going on three, years running so far (over on the eastern side of the metropolitan area they have had more rain as they usually do). Thus when I said that the bee was very tiny, I had in mind the size of the flowers which may have been closer to 5 to 7 mm in petal length.

This is why I've not been sure - I've compared what's here in my photos with both and am no further forward. But probably a Cuckoo Bee of either kind? Every bit helps, though.

Thank you, Hartmut, for this possibility, which seems to confirm my thoughts on the bee's species. And there I was, for so many decades thinking that there were but Bumble Bees and Honey Bees, never mind Cuckoos amongst them! Anyway, your help is much appreciated.