The pattern of the arms has now become more ragged than in ScI-II systems, but the arms are still moderately easy to trace. They are thicker than in ScI systems and cover a larger fraction of the underlying disk.
Although the range of absolute luminosities here is ~ 2 mag, again there is no appreciable difference in the appearance of NGC 5676 (the brightest) and NGC 1437 (the faintest). Note also that the surface brightness of the arm system (i.e., of the population I) is closely the same within this group and in fact is not fainter than for the galaxies illustrated in the ScI and ScI-II panels.
The two main inner arms in the barred spirals (NGC 4304 and NGC 2525) spring from the ends of the bar, as in NGC 1300 (Sandage, 1961, p. 45), and the arms are well defined for about half a revolution beyond their junction with the bar. However, in NGC 4304 especially, the arms beyond this point begin to fragment and decrease in surface brightness. The presence of these faint fossil outer arms becomes a common feature in galaxies of later luminosity class.
NGC 5676 W60-1999-H Sc(s)II -22m.11 2127 km/s | 
NGC 6643 P200-3064-S Sc(s)II -21m.64 1491 km/s |
NGC 4304 C100-225-S SBbc(s)II -20m.97 2608 km/s | 
NGC 2525 C100-779-S SBc(s)II -20m.92 1582 km/s |
NGC 2763 C100-789-S Sc(r)II -20m.48 1887 km/s | 
NGC 1437 C100-192-S Sc(s)II -20m.22 1162 km/s |