To me also they look like Rain Lilies. The leaves are there to show the clue too. It's very nice all of them are up at the same time - lovely anyway! In my garden they bloomed 4-5 days after an early summer shower in March.
I had posted a query - some clues may be there for you? --http://garden.org/thread/view/34331/Rain-Lilies---white---difference-between-two/