The invention concerns a bellows (7) designed to be coupled by a front end region (30) to a first rotary member (8) and by a rear end region (34) to a second rotary member (6). The bellows rear end region (34) is provided, over at least part of its periphery whereof the axial curve has a transverse contour with inflection points, a radially projecting lug (36) designed to be housed in a groove (20) of the second rotary member to retain axially the bellows rear end region (34) relative to the second rotary member (6), and sealing means designed to be supported on the second rotary member. The sealing means are axially located on the same side as at least part of the lug (36) retaining the bellows rear end region (34). The invention is applicable to tripod constant velocity universal joints.