Sadly, in his notes to Lolita (The Annotated Lolita), the otherwise seemingly erudite Alfred Appel Jr. believes that "auroch" is the singular of "aurochs", a word Nabokov uses in the all-important penultimate sentence of the novel.
I like phony umbrage as a concept and exercise a delight to work it into conversation from time to time. Phony umbrage taking is one of those "Pythonesque" aspects of Wordie that makes this forum so enjoyable, and endears certain contributors' posts and their phony umbrage to me.
Specie is also the surname of an attorney who represents creditors and serves as trustee in bankruptcy cases in my area. Said attorney gets to collect specie from the plaintiffs on behalf of the creditors. Yes c_b, I knew of the word specie - I cringe when the word is misused in a taxonomical sense.
HH is right: the singular form is aurochs, and according to my dictionary (useful things, dictionaries), the plural is the same, like deer. One aurochs, two aurochs, many aurochs. I would label this form a misspelling (and in fact I have done so).
Perhaps the -ochs is the singular, not the plural. Its an aurochs, not an "auroch", I'll wager. Maybe the plural should be "aurochsen", as in "oxen". Which might make auroch a back-formation of some sort.