A device for the selection and the displacement of actuation members (26, 30, 35, 41) of a gearbox for motor vehicles comprising a plurality of forward gear ratios (I, II, III, IV, V, VI) and a reverse gear ratio each associated to a respective actuation member (26, 30, 35, 41), the device comprising: - a selection mask having a pair of fingers (146, 147) opposite to one another and facing one another and a pair of through holes (148, 149) provided on said fingers (146, 147) and having axes which are coaxial and which define a main axis, - an engagement hub inserted between said fingers (146, 147) in a manner coaxial to said through holes (148, 149), said engagement hub having an engagement finger configured for engaging with said actuation members (26, 30, 35, 41) and being rotatable around said main axis, - a control shaft inserted within said through holes (148, 149) and into said engagement hub, said control shaft being rotatable around said main axis and axially movable along the latter, said control shaft being furthermore connected in rotation (157, 63) to said engagement hub, - a first control member connected in rotation to said control shaft and operable to cause a rotation of said engagement hub around said main axis to selectively displace each actuation member (26, 30, 35, 41) towards an extreme position thereof, - a second control member operatively connected to said engagement hub and operable to cause a translation of said engagement hub and said selection mask along said main axis to select the actuation member (26, 30, 35, 41) wherein said engagement finger is to be engaged, - a mechanism for the assistance to the engagement of the reverse gear that can be activated when said engagement hub is translated to engage the engagement fingers into the actuation member (41; 44) of said reverse gear, - guide means defining a guide path for said selection mask and configured to guide the selection mask so that the latter does not follow the rotation of the control shaft and of the engagement hub when a gear is engaged, the device being characterized in that said mechanism for assistance includes: - a first operative configuration wherein it is configured for setting up a deviation of the guide path so that during an axial travel of the engagement finger towards an extreme position preliminary to the engagement of the reverse gear the selection mask is forced to be temporarily displaced in a rotated position, wherein one of the fingers of the selection mask actuates at least one of the actuation members of the forward gears of the gearbox, so as to cause a halt of the rotation of the primary shaft of the gearbox and accordingly allow a subsequent regular and silent engagement of the reverse gear, and - a second operative configuration wherein it is configured for recalling said selection mask from said rotated position. - a selection mask having a pair of fingers (146, 147) opposite to one another and facing one another and a pair of through holes (148, 149) provided on said fingers (146, 147) and having axes which are coaxial and which define a main axis, - an engagement hub inserted between said fingers (146, 147) in a manner coaxial to said through holes (148, 149), said engagement hub having an engagement finger configured for engaging with said actuation members (26, 30, 35, 41) and being rotatable around said main axis, - a control shaft inserted within said through holes (148, 149) and into said engagement hub, said control shaft being rotatable around said main axis and axially movable along the latter, said control shaft being furthermore connected in rotation (157, 63) to said engagement hub, - a first control member connected in rotation to said control shaft and operable to cause a rotation of said engagement hub around said main axis to selectively displace each actuation member (26, 30, 35, 41) towards an extreme position thereof, - a second control member operatively connected to said engagement hub and operable to cause a translation of said engagement hub and said selection mask along said main axis to select the actuation member (26, 30, 35, 41) wherein said engagement finger is to be engaged, - a mechanism for the assistance to the engagement of the reverse gear that can be activated when said engagement hub is translated to engage the engagement fingers into the actuation member (41; 44) of said reverse gear, - guide means defining a guide path for said selection mask and configured to guide the selection mask so that the latter does not follow the rotation of the control shaft and of the engagement hub when a gear is engaged, - a first operative configuration wherein it is configured for setting up a deviation of the guide path so that during an axial travel of the engagement finger towards an extreme position preliminary to the engagement of the reverse gear the selection mask is forced to be temporarily displaced in a rotated position, wherein one of the fingers of the selection mask actuates at least one of the actuation members of the forward gears of the gearbox, so as to cause a halt of the rotation of the primary shaft of the gearbox and accordingly allow a subsequent regular and silent engagement of the reverse gear, and - a second operative configuration wherein it is configured for recalling said selection mask from said rotated position.