I tell this story in case it helps somebody.  Also, maybe, somebody will tell me a better way.

I run some Fury's and Zeus Blizzards on cgminer 3.1.1.  My command line names the com ports of each Fury specifically like this:

.....  -S //./COM260 -S //./COM266

and so on.  Today I added my 10th Fury, and after I hooked it up, cgminer would not start!  I unplugged the new device, no change.  ...Because I had moved the miners around to different hubs and such over time, I had a few com ports listed that had no Fury's hooked to them, so each time I start cgminer it says like "cant connect to com 170..." and such.  On a hunch, I removed my four non-existent com ports from the command line, and now cgminer starts just fine.  My conclusion:  There is a limit to how many com ports you can specify on the command line of cgminer 3.1.1.  It would seem the limit is 13.

(Somebody who can READ might already have known this fact