Dear Olivier:
I believe that this is Gromphas !!. This genera has 4 species, one of it is very rare and not very well-known:
Gromphas lacordairei Brullé, 1834
Gromphas aeruginosa Perty, 1930
Gromphas dichroa Blanchard, 1843
Gromphas amazonica Bates, 1870 (very rare)
I believe that tihis specie maybe Gromphas lacordairei ? Brullé. but I am not very surely. I have two species in my collection (G. aeruginosa and G. lacordairei) and I will compare these with your picture
I will revise the literature because I have some articles on them, but this it is not the same picture that you showed me before !.
My regards
Carlos