The following new scarab beetles are described from South America: Cyclocephala dupuisi Ratcliffe, new species, from Bolivia and Stenocrates caiporae Ratcliffe, new species, from Brazil (both Cyclocephalini); Hiekeianus halophilus Ratcliffe, new species, from Peru, Neoryctes similis Ratcliffe, new species, from Ecuador, and Adelaeus anachoretus Ratcliffe, new genus and new species, from the Galápagos Islands, Ecuador (all Pentodontini); and Hemiphileurus cornutus Ratcliffe, new species, from Colombia (Phileurini). Each new taxon is provided with a description, supporting illustrations, a diagnosis to distinguish it from similar taxa, and distribution. A revised key to the genera of New World Pentodontini is provided to include Adelaeus.