Proserpina

Asked to name the planets outward from the Sun, James Blish's juvenile hero, Chris deFord, recites:

"'Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Proserpina.'"
-James Blish, A Life For The Stars IN Blish, Cities In Flight (London, 1981), pp. 131-234 AT p. 150.

When I first read A Life For The Stars, as a juvenile reader, I had learned the planets and knew that none had yet been discovered beyond Pluto. This was decades before Pluto was demoted, of course. Later in Cities In Flight, the City Fathers (computers) tell the Mayor of New York who, surprisingly, had not known this, that:

"'PROSERPINE IS A GAS GIANT, ELEVEN THOUSAND MILES IN DIAMETER, OUTSIDE THE ORBIT OF PLUTO...'"
-James Blish, Earthman, Come Home IN Cities In Flight, pp. 235-465 AT p. 411.

So Earthmen say "Proserpina" whereas Okies say "Proserpine." I think that an Arthur C. Clarke novel named the tenth planet "Persephone" but no way do I know which novel. (Greek: Persephone; Latin: Proserpina or Proserpine.)

In Poul Anderson's The Stars Are Also Fire, Venator thinks that it is necessary that "...Proserpina be forgotten." (25, p. 336) Later in the text but earlier in this future history, Dagny Beynac suggests that a newly discovered remote planetoid be named "Proserpina" (26, p. 357) and the reader thinks, "So that's it!"