You can find this exercise on page 56 of the book Synergistic Golf.
Exercise Type: PILATES
Exercise Category: ABDOMINALS, FLEXIBILITY, LEGS - FEET, RHYTHM - TIMING, STRENGTH
Start with upper spine flexed off mat with belly button pulled into spine. Extend one leg toward sky and reach other leg parallel with floor. Hold on to raised leg. Exhale as you switch legs like scissors maintaining a flat back and abdomen tight. Focus on the lengthening of legs and engagement of midsection. Repeat 10 times.