Differences between a fovea & area centralis?

[Michael Hucka]

Can someone please explain to me the differences between a fovea and an area
centralis?  I know which species have which kind, and understand that a fovea
is a pit-like depression containing only tightly-packed cones and with the
bipolar and ganglion neurons shoved out to the surrounding area.  But I've
had some difficulty finding a description of an area centralis and how it
differs from a fovea.
--
   Mike Hucka (michael.hucka at umich.edu)
   University of Michigan, Ann Arbor, Mich.