When are mummies mentioned in Catcher in the Rye?

Chapter 25

While I was waiting around for Phoebe in the museum, right inside the doors and all, these two little kids came up to me and asked me if I knew where the mummies were. The one little kid, the one that asked me, had his pants open. I told him about it. So he buttoned them up right where he was standing talking to me--he didn't even bother to go behind a post or anything. He killed me. I would've laughed, but I was afraid I'd feel like vomiting again, so I didn't. "Where're the mummies, fella?" the kid said again. "Ya know?"