The open cluster Dunlop 358 = Trumpler 23 (top left in attached image) is "A pretty large faint nebula, of an irregular figure, about 6' diameter, very faint" according to Dunlop. The nebulae Gum 50 = RCW 99 (lower right) is 17' from it.
Dunlop catalogued 3 objects on 1/7/1826, the OC Tr23, the PN NGC 5189 and the OC Lac I.7 = NGC 5281.
The image is from
http://www.wikisky.org/ See also
http://galaxymap.org/cgi-bin/rcw.py?s=91
Trumpler named the OC Tr23 104 years later in 1930.