This gomphid was regularly seen in some parts of the river Cristalino, at least in July. They often came to sit on the boat.
I think it is a Progomphus species.

23/01/2008
I also tried to identify this species today, but my photos on the internet didn't allow me to say for sure if the gomphid in the picture has a basal subcostal crossvein. Now, back home, taking a better look at the originals, I can tell that it has a basal subcostal crosvein in both fore- and hindwing. I will add some pictures of details soon and then try again.

9/8/2008
Following the key in Heckman (?!) on the basis of these photos I come to Progomphus intricatus, which should occur in Para and Mato Grosso, Brazil (among other places). Maybe this could be Progomphus intricatus. I will compare with specimens (if they have that species) next time I am in the museum.