Hi Jorge I would say that it is a Corydoras Ellisae or possibly a Corydoras Garbei but more than likely Ellisae. The Corydoras Diphyes has a lot more markings than the fish in the photos.
Do you have any idea where the fish were exported from, this would help a great deal. They do look a little like C. ellisae but they are also very much like a species I have that come from Argentina, and a very prominent character is that they have very heavy serration's on the posterior edge of the pectoral spines, which is fairly easy to see.
Hi jorge: Yes, that´s help to id. But coryman you should do it with the fish that you received from Argentina because should be the same. Here the corys are:
C. paleatus
c. undulatus
c. macropterus
c. microps??
c. aff aeneus
And then we have in the same area:
C. polystictus
C. aff elisae (the fish in the picture)
C. sp "longnose"
There are no other corys in that area, and generally all are fished copmercially in a unique river.
A german friend said that was elisae, but could be something else of course.
As far as I can see these are the same species that I have, information from the guy that actually collects and exports them tells me the location is the same as C. polystictus in the Parana River Drainage south of Corrientes City.
C. ellisae comes from a relatively small area in southern Paraguay, the major difference between the two species are the heavy serration's on the posterior edge of the pectoral fin spines in the Argentina fish.