When the two B-spline boundary curves of the ruled surface are in two parallel planes,a necessary and sufficient condition for a developable B-spline ruled surface of degree(n,n+1)is derived,and the developable B-spline surfaces of degree(2,3) are constructed.A necessary and sufficient condition for a developable B-spline convex ruled surface of degree(n,n+1)is obtained.A few developable B-spline r...