Thanks for the reply. One error was that I thought the Arduino program would recognize the USB port even without the Arduino board powered.
I have the Little Bits Arduino at heart board.
Now, I am able to see the port once the board is powered on.
It still does do something odd… when I upload the sketch to the board, the computer behaves as if I plugged in a keyboard. I.e., the Mac OS brings up a screen asking me to identify the keyboard just plugged in. It doesn’t seem to interfere with the operation of the Arduino board otherwise… but I admit I don’t have a very good way to ‘test’ things (from lack of grasp!).
I think, putting that anomaly to the side, that it works… the sketch presently seems to be driving the board, and it is transmitting what the code instructs to further bits of circuitry.