I'm cleaning obsolete files off my computer and have discovered saved webpages about the records Harvard holds about some defunct Universalist and Unitarian churches. There's no good reason to save the cached pages; you can read about the holdings yourself here.
But why look? To feel miserable about what's lost? No. To see the stream of mergers and consolidations. Turns out that the Fifth Universalist Society, Boston, changed buildings and names in a snail-like crawl from Boylston Hall, to Shawmut Avenue, to Brookline, to Waltham, where merging with another church expired in 1946. (Or perhaps not, the records got to Harvard in 1982 via the First Parish, UU, Waltham, so perhaps there was a final merger.)
The Shawmut Avenue era, as the Shawmut Universalist Parish, is the most glorious era as described in chapter 27, volume 2 of Miller's The Larger Hope. The minister was George L. Perrin, recently returned from the Japan mission and he set about making the church "the Every-Day Church" or the kind of institutional church that responded to the community by providing social services. The Bethany Union -- in case you've seen it in the UUA directory and wondered what it was -- survives from this church's members in this era.