This isn't as much of a singular move as it is a series of transitions that you should practice.
When you get a mount, and your opponent immediately begins to shrimp out, if you're not very good at keeping your mount, it may be a better idea to move off into side control rather than get trapped in half guard/closed guard after you've worked so hard to get a better position.
I'll run you through the first 1/2:
-Start in mount
-Opponent begins to frame/elbow his way into an escape
-As your opponent begins to turn towards your leg, throw your arm diagonally over his head, and plant your elbow on the floor to trap it. This way, you have a good range of movement with that arm.
-Post out with the other hand, and with that side's leg, throw it over the other side to get to side control. Drive that knee to the hip, then get the posted hand over to the hip as soon as possible to sprawl and establish your position.
-To move to a north south, post the hand that's on his hips straight down to the floor to continue blocking his movement while you switch your hips, and being the leg closer to the hips up to his shoulder, then toss the other leg over that one to establish north-south.
-Continue, except reversing the steps to get to side control on the other side, and back to mount after that.