I wasn’t really asking about the “correct” use of latin. Although that is important when creating the names to try and get that right.
But the question was really what is the correct spelling to use, once the name has been created and published. The original publication of this name, as I looked up in the original source, was “Agaricus calyptraeformis”, so I was told after that the correct spelling is and always should be “calyptraeformis”, whether or not this is correct latin, that is what was done.
But at some point the spelling turned into “calyptriformis”, and this spelling is listed as preferred by Index Fungorum at least. I want to know is there some rule in the use of the proper name, that allows the change of spelling like this. Does anyone know?
There are the cases where the genus changes, and the ending of the name then changes to agree with the genus, a “-us” to an “-a” or such. But I don’t think that would effect the changing of the spelling in the middle of a name.
If it is correct latin or not…
I’m not sure about the “( :Fr.)” question there, that doesn’t seem to be an issue here at all? The species was first published by Berkeley, in a date after the first sanctioning work, so the author here should just be “(Berk.)”. Fries had nothing to do with this one at least.