A nice little armbar, not aware of any other name:
Assuming you're facing the same direction as the turtled opponent, slip the right leg through and hook the foot around the outside (opponent's left) leg. With the head posted, reach around the guy's right arm and grap your own gi lapel. At the same time, shove his head down with your left hand and get your left leg under it. Roll to the right, lift hips. and voila.
edit - grammar.