By default OSX does not show other devices on the Desktop. Part of Steve Jobs' Zen thing I suspect. You can easily enable it.
Make sure "Finder" appears next to the black Apple at the left end of your menubar. From the Finder menu select "Preferences." You will get this:
Make sure all the boxes under "Show these items on the desktop" are checked.
Now see if your card shows up.
Some cards may only be recognized by Image Capture in your Utilities folder.