From the same site under "A. Japonicus" -
The powder brown is similar to the Gold Rim Tang (Acanthurus nigricans).
under A. Nigricans
Gold Rim Tang, Powder Gray Surgeonfish, Whitecheek Surgeonfish
The Gold Rim Tang is less frequently available than the similar Powder Brown Tang.
So the information presented is a little inconsistent but my pocket guide by Scott W. Michael - Marine Fishes - ISBN 978-1-8900-8738-8 clearly states A. Japonicus as Power Brown and A. Nigricans as Whitecheek.
The easy of care rating at
www.themarinecenter.com for A. Nigiricans is higher than A. Japonicus.
From the animal-world.com
When purchasing this tang, you will want to be sure you are getting the correct species. Both the White-faced Surgeonfish and the Gold-rimmed Tang (Whitecheek Surgeonfish) A. nigricans are regularly sold as the 'Powder Brown Tang'. Though they look very similar the White-faced Surgeonfish will show a pronounced "white-face" along with its red stripe on the dorsal fin, these markings will be lacking on the other. Also the White-faced Surgeonfish is a relatively hardy aquarium inhabitant once acclimated while its almost 'look-alike' cousin is more difficult to sustain in captivity.
http://animal-world.com/encyclo/mari.../japonicus.php
The wet-web media site description is a little different from the rest..
http://www.wetwebmedia.com/GoldRimSs.htm
But between two, A. Japonicus has a lot more brown in color, and if it fares better than A. Nigricans, I can't really complain about it, as I like A. Nigricans better and that's what I consider a Powder Brown tang
