If so what's a good substitute?
ABsolutely! If you bought them at the supermarket, most likely they came ina box with tightly covered plastic wrap. Leaving them wrapped like that is an invitation to slimey mushrooms. Instead, they'll keep better, longer if you transfer them to a paper bag. I label them with type of mushroom and the date if I don't plan to use them the same day. I ahve found that when stored in paper bags, they usually keep well for a good week.
Storing them as June suggests is important. If the mushrooms are wild mushrooms watch to make sure that there are no worms in them. That's why large porcini are often cut in half and banded together. I complained to the farmers' market seller about some I had a problem with and she said to just put them in the sun for an hour!