Tonight I was looking for my floppy drive device to use with dd on my macbook. OS X is based on Darwin which is a BSD port but apple has changed up the /dev device names from the usual BSD ones. The easy way to find out a /dev/devicename entry is to open System Profiler and to find the device listed and click on it.
For example, my usb floppy drive was listed under Hardware > USB > USB Floppy. Once I selected that the information window lists all kinds of details about the device, including the “BSD name” which in my case was disk2. So the dev entry for my floppy disk is /dev/disk2. It’s a lot easier than guessing!