Exist genuses?

[Barry Roth]

I have just finished reading Nabokov's Blues: the Scientific Odyssey of a
Literary Genius" by Kurt Johnson and Steve Coates (1999, Zoland Books).
The title refers to the fact that the novelist Vladimir Nabokov was a
taxonomic lepidopterist ("blues" referring to the category of small
butterflies).  I won't review the book here, but one use of the English
language brought me up short:  throughout the book, the word "genus" is
pluralized as "genuses."

I asked a friend of mine, a professional editor, and he referred to it as
"a barbarism."  I have never encountered "genuses" anywhere else, but maybe
I'm missing a trend.  Anybody?

Barry Roth