We study the one-dimensional solution of the shape equation of bilayer membranes within the Helfrich spontaneous curvature model. The general integral of the cylindrical shape equation is obtained which gives a complete classification of the cylindrical surfaces corresponding to the shape equation. For closed vesicles, they are inward noduloids, outward noduloids, alternatively inward and outward noduloids and polygonal shapes. The curvature of the contours of the cross sections of these surfaces can be expressed in terms of elliptic functions of their arc lengths.