in the micro photos probably rules out Pluteus.

This speciemen lived in the same branch of the fallen tree that the one in MO67170, although clearly is not of the same species. In the soil developed what I think is another Bolbitius species, the one in MO67168. After one week, when I made other observations at the same place, I found the Pluteus considered in MO67283, again in the same branch of the fallen tree.
Concerning this specimen, maybe it is not a Bolbitius (notice that the value of Q for the spores is different from the other two – MO67168 and MO67170). I think that Pluteus is also not to exclude for the specimen in this observation.

of the spores and color don’t rule Bolbitius out, but it’s not clear to me what supports the identification as Bolbitius

Is this from the same branch, ie. the same species? It doesn’t look very similar, but perhaps I’m mistaken.

Please see the comment posted in 17/05/201 in Observation MO67170.
For the specimen corresponding to this observation, I got the following results for spores:
7.4 [8.2 ; 8.5] 9.3 × 5 [5.7 ; 5.9] 6.5
Q = 1.3 [1.4 ; 1.5] 1.6 ; N = 42 ; C = 95%
Me = 8.37 × 5.77 ; Qe = 1.45
It seems that the genus can be Bolbitius.

viscid, and the gills are a bit dull – maybe Simocybe?