I took one out last week, its a GE 1251. The base has one conductor on the bottom, and the sides have two posts that twist into the receptacle (bayonet style?).
Quick note.. don't try and take these out or put them in while the light system is energized, even wiggling them can cause some nice arcing/sparking which can melt the plastic spring loaded base behind the bulb and cause you to have to buy a new housing.