Ian Fuller, at his site corydorasworld.com, has this to say about C. schultzei:
"The type material for this species has been lost and therefore it is extremely difficult to be certain of its validity, although there are distinct characters which would suggest it is a valid species. Science considers this species to be a synonym of C. aeneus.
Bred under aquarium conditions, the species known as the 'Black Cory' was developed from this species after a number of black fry emerged from successfull spawnings."
When I first saw them, I thought they may be black corys.
HTH!