The specific name minor was first used by Herbst (1782), although no specimen is extant and it is not at all clear which species he was referering to. One could reasonably assume that he was using minor to refer to the traditional Cancer vocans, in contrast to the larger form he designated as major. If so, Uca minor would be a junior synonym of Uca vocans.
The name was later independently used as Gelasimus minor Owen, 1839, to describe a species from Hawaii. No fiddler crabs are found on Hawaii, but a variety of details point to this being collected further west and likely representing Uca perplexa (H. Milne Edwards, 1852). Since Gelasimus minor Owen, 1839, is a clear junior homonym of Cancer vocans minor, it was unavailble to Owen and does not take precedence over Uca perplexa.