Choosing correct transistor for simple Arduino 9V power switch
Typically you want a simple low side NPN switch setup. A high side switch would complicate things as your arduino cannot accept higher than 5v at it's input pins (or whatever VCC is).

A NPN like the 2n3904 or 2n2222 is all you need. Common workhorses for small signal. You know your target load of 360 ma, and they both have a worst case gain of 30. You would connect the 9V to your motor and the motor to the collector and the emitter to the common ground between your arduino and the 9V battery. 

You would connect the base to your gpio with the appropriate base resistor. 470 ohms should do nicely for the base current needed.

As a suggestion,  you are wasting half your power in the 50 ohm resistor. As you are turning all of them on with a single pin, you should be able to sixtuplicate your battery life by putting the motors in series pairs without any resistors. Two motors in series should equally divide the input voltage between them. 

Additionally, a diode being used as a flyback protection diode across the motors would be ideal, as suggested by SP.







simulate this circuit &ndash; Schematic created using CircuitLab