| Abstract | H I observations are presented for 13 supermassive spirals. The 20 percent profile width of UGC 9255 (NGC 5619) at 750 km/s is among the largest reliably recorded for any galaxy and is the largest for an Sb. Comparison with the other well-observed objects with wide profiles, NGC 4594 and NGC 5635, shows that it has a diameter 50 percent larger than the first and a more than 1.5 mag greater brightness than the second. In relation to a comparison group of supermassive galaxies, however, UGC 9255 is normal. An improved adjustment to the Zwicky apparent magnitude is derived for low-surface brightness galaxies. |
