Heinrich d'Arrest discovered NGC 2931, along with NGC 2929 and 2930 on 21 Feb 1863. His position, measured on 3 nights, matches CGCG 122-036 = PGC 27415. He noted a mag 14-15 star (mag 12 in my observation) follows by 11 seconds of time.

400/500mm - 17.5" (4/15/93): third of three with NGC 2930 2.5' SSW and NGC 2929 5' SSW. Faint, fairly small, elongated 3:2 WSW-ENE, weak concentration. A mag 12 star is 2.6' E.

600/800mm - 24" (2/15/18): at 375x; fairly faint, fairly small, slightly elongated WSW-ENE, 40"x30". Third in a collinear trio with slightly fainter NGC 2930 2.5' SSW.

Notes by Steve Gottlieb