First you must learn to view the spore sculpturing with cotton-blue dye (preferably C4B, dissolved in lacic acid, though many people use lacto-phenol). Gentle heating to the boiling point helps intensify the stain. Then you need to consult the important monograph of Trond Schumacher (Norway); Schumacher T. 1990. The genus Scutellinia (Pyronemataceae). - Opera Botanica 101: 1-107. That has keys and good descriptions of microscopic characters, hairs, etc., and both line drawings and scanning microscope photographs of the spores that should allow you to make determinations in this difficult genus. Of these three, S. umbrorum will be the easiest to recognize, with the differences between S. scutellata and S. crinita more subtle. Good luck!

Dick