The proton flare of 1973 September 7 was a classical long duration event associated with a filament disruption and coronal transient. The flare images show a compact, nearly cylindrical arcade centered along the filament channel and composed of four prominent loops. Comparison of loop arcades in ions of different temperatures reveals a pronounced shell structure: the loop systems of Fe XII (Te = 1.4 × 106 K) and Fe XIV (Te = 1.8 × 106 K) are smaller than, and lie nested within, the arcades of Fe XVI (Te = 2.2 × 106 K) and Ca XVII (Te = 5 × 106 K). The expansion of the loop system in various ions was determined by measuring the separation of the loop endpoints. The loop arcades at different temperatures, as well as different loops within a given arcade, show different expansion rates. These vary from 6 to 8 km s-1 for Fe XIV shortly after flare maximum to 0.5-1 km s-1 late in the decay phase. For hotter ions, such as Ca XVII, the velocities are approximately constant at 2-3 km s-1 during the whole of the observations.