OK, wanna see something odd?
If you go to this URL:
http://www.geology.gla.ac.uk/palaeo/nmita/database/bivalves/systemat/bivalgen.htm
you get a list of "Neogene" bivalve genera of tropical America, and on
that list, in alphabetical order, is the genus Acropsis!  Farther down
the list is Arcopsis.
BUT - and here's the strange part - at first I thought I was seeing
things . . . scroll to the bottom of the page, click on bivalves, then
click on Taxa (Genera)
The same list reappears, only now Acropsis has been changed to Arcopsis.
 It still occupies the same place in the alphabetical list (now out of
order), and Arcopsis still appears farther down the list, where it was
before.  Odd, no??
Paul M.