William Herschel discovered NGC 4366 = H III-97 on 13 Apr 1784 (sweep 191) and recorded "Two unequal nebula [the other is II-144 = NGC 4370]; one of them [III-97 = NGC 4366] eF." Dreyer notes that III-97 was observed one only 1 sweep and not seen again when nearby II-144 = NGC 4370 was reobserved on 28 Dec 1785. It was also not seen by JH, d'Arrest, or by Samuel Hunter with the 72". So, Dreyer suggested NGC 4366 = NGC 4370 and this was repeated by Dorothy Carlson in her 1940 list of NGC errata.

But 5' northeast of NGC 4365 is CGCG 042-087 = PGC 40421, a faint galaxy that WH might have picked up. This galaxy is identified as NGC 4366 in the RNGC, PGC and Deep Sky Field Guide though not in CGCG or MCG. But this galaxy is slightly further from NGC 4370 than NGC 4365, so it seems odd WH would record it together with NGC 4370. So, the identification NGC 4366 = PGC 40421 is very uncertain.

400/500mm - 17.5" (3/28/87): very faint, small, diffuse, even surface brightness. Located 5' NE of NGC 4365.

Notes by Steve Gottlieb