Leonardo not listed under Serial Ports on OS X

I've got a Leonardo R3 and OS X 10.8.3 and IDE 1.0.5. The device is not shown under the Serial Ports menu, and ls -l /dev/tty.usb* finds nothing. dmesg shows some log messages that I think are related to the Leonardo ("The USB device ATm32U4DFU (Port 2 of Hub at 0xfd100000) may have caused a wake by being disconnected"), but otherwise there's no sign that it's connected. The LEDs are on. I've tried both USB ports and two different cables. Where do I go from here?