A gearbox having a housing and a fan which brings about an air flow, wherein the housing has a lower housing part and an upper housing part, wherein the upper housing part is placed upon the lower housing part, wherein the gearbox has an input shaft, wherein the lower housing part and the upper housing part contact along a contact surface, so that the contact surface lies between the lower and the upper housing part (1, 4), in one plane, characterised in that the fan is arranged at the gearbox and connected to the input shaft in a rotationally-fixed manner, such that the air flow brought about by the fan is axially directed, wherein cooling ribs adjacent to one another in an axial direction are arranged at the housing, which ribs are curved in such a manner that a portion of the air flow flowing along the housing and directed axially, therefore parallel to the rotational axis of the input shaft of the gearbox, is in each case deflected in a respective transverse direction between two cooling ribs next-adjacent in an axial direction, wherein a first number of the cooling ribs are arranged above the contact surface, a further number of the cooling ribs are arranged below the contact surface, wherein the cooling ribs arranged above the contact surface deflect the respective portion of the air flow in a transverse direction and the cooling ribs arranged below the contact surface deflect the portion associated in each case in a direction directed counter to the transverse direction, wherein the initial spacing of the cooling ribs in an axial direction decreases monotonically, wherein the initial spacing of the respective cooling rib is in each case the smallest spacing of the cooling rib from the contact surface, wherein the axial direction is parallel to the contact surface, wherein the cooling ribs are two-part or multi-part in each case, wherein a respective first part of the cooling ribs is formed on one of the two housing parts (1, 4) and a respective further part of the cooling ribs is formed on a bearing cover of the gearbox. wherein the housing has a lower housing part and an upper housing part, wherein the upper housing part is placed upon the lower housing part, wherein the gearbox has an input shaft, wherein the lower housing part and the upper housing part contact along a contact surface, so that the contact surface lies between the lower and the upper housing part (1, 4), in one plane, characterised in that the fan is arranged at the gearbox and connected to the input shaft in a rotationally-fixed manner, such that the air flow brought about by the fan is axially directed, wherein cooling ribs adjacent to one another in an axial direction are arranged at the housing, which ribs are curved in such a manner that a portion of the air flow flowing along the housing and directed axially, therefore parallel to the rotational axis of the input shaft of the gearbox, is in each case deflected in a respective transverse direction between two cooling ribs next-adjacent in an axial direction, wherein a first number of the cooling ribs are arranged above the contact surface, a further number of the cooling ribs are arranged below the contact surface, wherein the cooling ribs arranged above the contact surface deflect the respective portion of the air flow in a transverse direction and the cooling ribs arranged below the contact surface deflect the portion associated in each case in a direction directed counter to the transverse direction, wherein the initial spacing of the cooling ribs in an axial direction decreases monotonically, wherein the initial spacing of the respective cooling rib is in each case the smallest spacing of the cooling rib from the contact surface, wherein the axial direction is parallel to the contact surface, wherein the cooling ribs are two-part or multi-part in each case, wherein a respective first part of the cooling ribs is formed on one of the two housing parts (1, 4) and a respective further part of the cooling ribs is formed on a bearing cover of the gearbox.