Kathy, your pictures are wonderful!
I believe you can rule out lacera, I don't think it would be that white.
Paul Martin Brown ( Wild Orchids of the Northeastern United States, a field guide) puts the blooming time for blephariglottis to June 28. - August 25. And the height 15 - 60 cm. Sounds promising!
Blooming time for clavellata is June 8. -August 29. But he gives the color as green to straw yellow.
Brown also lists Platanthera dilatata as white, and blooming time is June 10. to September 5, height 30 -108 cm.
This one is supposed to smell of cinnamon.
