This seems potentially backwards to me. If we apply a voltage source across the terminals, parallel coils between the terminals would result in higher voltage across each coil than would series coils. With series coils, the total voltage applied would be divided between the coils.
I'm looking at it as a total system. You've got, say, a 12V battery with some internal series resistance. And, say, the two coils are 6 ohm each. Let's say the internal resistance of the battery is 1 ohm, arbitrarily.
If the two coils are in series, you'll have a total coil resistance of 12 ohms (13 ohms incl internal resistance), and will get 0.923A (12V/13ohm) through the motor, with a terminal voltage of 11.07V (12V x 12ohm/13ohm).
If the two coils are in parallel, you'll have a resistance of 3 ohms, and a current of 3A through the motor (12V/4ohm), and a terminal voltage of 9V (12V x 3ohm/4ohm). Lots more current, but lower terminal voltage.
Could someone clarify?