Donald Antrim is, after Thomas Pynchon, American literature’s presiding weirdo. He’s a trickster. His books are short, vivid, drastic and surreal, so much so that reading them is like driving 90 miles an hour while in third gear, in the back seat of a jalopy the author has stolen, while he disposes of his drugs by throwing them out the window.

Mr. Antrim has lately begun to downshift. After delivering three very fine and very antic novels — one is about a psychoanalyst who levitates to the ceiling of a pancake house, another about 100 brothers packed into a room — he published “The Afterlife” (2006), a tender memoir about his mother, an eccentric and volatile alcoholic.

His new book, “The Emerald Light in the Air,” is his first collection of short stories, and his first book since winning a MacArthur fellowship — I recently heard one of these referred to as a Big Mac — in 2013. Here, too, the mood is a bit more restrained, as if a yoga instructor had begun to teach Mr. Antrim how to breathe. I will not accuse him of mellowing. If his plotting is less berserk, his prose is as exacting as ever.

The bad news about “The Emerald Light in the Air” is that it’s decidedly hit and miss. Middling stories outnumber keepers. Mr. Antrim’s lesser stories noodle around for many pages, then drift off rather than end.