which is depressed from the top surface 110 of the carousel 24 the floor 108 is surrounded by sidewalls 112 and 114 and an end wall 116 which extend from the floor 108 to the carousel surface 110 the end of the berth 54 opposite the end wall 116 is open to serve as a port for insertion of a cartridge into the berth 54 the aperture 56 is located within the floor 108 shoulders 118 extend from each of the sidewalls 112 and 114 in a direction generally parallel to the floor 108 to form grooves 120 between the shoulders 118 and the floor 108 the locations of the shoulders 118 are retracted from the ends of the sidewalls 112 and 114 towards a more central location of the sidewalls 112 and 114 an outer circular surface 122 of the carousel 24 is provided with a chamber 124 at the site of the berth 54 the chamber 124 extending along an interfacing edge of the surface 122 with the floor 108 and each of the sidewalls 112 and 114 of the berth 54 the chamber 124 facilitates alignment of the cartridge 22 with a berth 54 during insertion of the cartridge 22 into the berth 54 by the injector 58 fig1 in accordance with the invention the ledges 92 and 94.