From:  Frenchy Pilou (PILOU)
2511.6 In reply to 2511.5 
This sort of surface is an headache :)
Even with the Jotero solution very difficult to refind it!
It's a square, and the base arc circles are corner center to middle edges
Seems internal curvatures can be as you want
Not yet remake :) I must study more in depth :) But I am very slow minding :)
Not sure of the straight line

EDITED: 27 Mar 2009 by PILOU