Two new species are described that are remarkable in having exaggerated female genitalia: Mesabolivar samatiaguassu sp. n. and M. cuarassu sp. n.. Comparative evidence as well as size measurements of male and female structures suggest that the exaggerated female external genitalia correlate functionally with elongated male cheliceral apophyses. These morphological findings are discussed in the light of competing models of genital evolution. Luring mating acts, female cooperative behaviour and morphology, as well as the probable costs associated with the female structures argue against the antagonistic coevolution model and favour sexual selection by cryptic female choice.