Howe suggested, and a short note from Swift published by Howe in Monthly Notices for 1899 seems to concur, that NGC 4740 is actually NGC 4726. But Tempel's observation of N4726 (which see) clearly rules this out – he places N4726 just four arcmin north of N4724 and N4727, a close pair found by the Herschel's. With IC 3834 being another 45 seconds of time east, it's extremely unlikely to be Tempel's galaxy.
Bigourdan did not find NGC 4740 at its NGC place, of course. I checked the other nebulae found by Swift that night – there were none, at least found by Lewis Swift. His son Edward, then a teenager, actually found four new nebulae on the 27th: NGC 4544, 4633, 4969, and 5309. With the exception of N5309 (which see), these all follow Swift's positions by about 18 seconds of time, and are south by about 30 arcsec (N5309, assuming we have the correct galaxy, follows by 29 seconds, but has a 10 arcmin digit error putting it south by 9 arcmin 10 arcsec).
I don't think we can make much of this comparison with the mean offsets, though, since N5309 also breaks the pattern, and since N4740 was the only galaxy which Lewis Swift himself found that night.
However, of the four galaxies in the area, NGC 4727 – by far – comes closest to fitting Swift's description. Thus, I am, in spite of a few misgivings, I am pretty well convinced that NGC 4740 is just another observation of N4727.