So, according to Steam, XCOM: Enemy Unknown has 60 achievements, whilst the Xbox Live version only has 50. None of the extra achievements have descriptions, and according to Steam, no one has completed them yet.
Giant Bomb, however, does have descriptions (I have no idea where they came from) listed for each of these, as follows:
"All Aboard: Complete Confounding Light with more than 3 turns left on the timer."
"The Bigger They Are: Complete Gangplank"
"Bait The Hook: Complete Confounding Light"
"New Friend: Complete Friends in Low Places"
"Rising Dragon: Take Your New Ally Into The Final Challenge"
"Disaster Averted: Complete Deluge"
"No Sweat: Complete Deluge Without Activating More Than 2 Valves"
"Saved To Savior: Have your newest ally volunteer for the most difficult duty."
"Great Minds Think Alike: Complete Furies"
"The Chase Is On: Complete Portent"
So, what could these mysterious achievements be, and why are they not available on consoles? Speculation? Conspiracy theories? Something your friend's cousin who works at Nintendo told you? I'd love to hear it.