Family Coreidae, Subfamily Coreinae, Tribe Hypselonotini, Anasa lunicollis
A good description (in spanish) can be found here: https://books.google.com.br/books?id=MN5...
Although first described in 1855, it looks like this is a very rare bug. These ones were found in a secondary forest, in the outskirts of Curitiba, Pr., Brazil.
My friend Bolívar Rafael Garcete Barrett provided me an ID for this bug, wich I reproduce here: "In fact its head reminded me of Anasa. There is a little bunch of horned species of Anasa and this is a very rare one. Brailovsky (1985) records it from Nova Friburgo (Rio de Janeiro) e Nova Teutônia (Santa Catarina) and says it is found at altitudes between 300 and 500 masl, but in fact Nova Friburgo is above 800 masl, as well as Curitiba, which is above 900 masl. Amongst the horned Anasa, this species is readily diferenciated by the netlike pattern of the corium and the distinct black scutellar stripe."