I wouldn't normally discuss a coin up for sale, but I don't think this one is going under the radar !
Not exactly an LRB of course, but that's why it's interesting. I thought Bastien only collected LRBs and provincials, but then there's this 2 solidi medallion which seems it must have been a major outlier in his collection. This is NAC 125.879 with an estimate of 50,000 CHF, and is the (unique?) RIC 167 specimen known to RIC. Berlin has the same type but with an obverse legend (RIC 166) vs this anepigraphic one.
This coin was the subject of a 1958 paper by Bastien "Médaillon d'or inédit de Constantin II", which can be found online.
The LRB portion of Bastien's collection was sold partly in M&M 61 in 1982, and party privately to the ANS in 1984. The M&M sale didn't even mention Bastien's name, but seemed to only be referring to the LRBs as his, not the solidi that were also in the sale. I wonder if this medallion was ever sold, or perhaps is only now being sold by someone he left it to ?
Bastien was only an amateur numismatist. His real job was surgeon, and in one of his obituaries someone recalls him saying how he would spend his appendectomy fees on coins (presumably LRBs and provincials), so this medallion must have represented quite a lot of scalpel work!
Ben