Which Shape On Which Card?

Jemima has 5 cards which are numbered 1 to 5 on one side, and either have a square, a circle, a triangle or a star drawn on the other side. She knows that there is at least one card with each shape and that odd numbered cards do not have squares on them. Card number 4 has a circle on it, and two cards that have a sum of 6 both have stars on them. What shape is on card 3?