Mylesinus is a genus of pacus in the piranha family Serrasalmidae, distributed across Amazon and Orinoco river systems and Guiana Shield drainages - the atlas records it from Brazil, Guyana, Peru, and Venezuela. Atlas species range from about 4.5–14 in, and like other serrasalmids they carry a deep, laterally compressed body and a single row of sharp, mostly herbivorous teeth adapted for cropping fruit, seeds, and leaf material that falls into flooded-forest waters.
Mylesinus schomburgkii, Schomburgk's silver dollar, is the species most likely to be encountered by aquarists, occasionally offered to large-tank keepers wanting a big herbivorous pacu alongside other serrasalmids; the other two atlas species are rarely if ever seen in the trade. Care follows general large-serrasalmid practice - roomy tanks, strong filtration, and a vegetable-heavy diet, since a hungry group of pacus will strip a planted tank fast. Two of the three atlas species are Least Concern and the third has not been evaluated.