Primocerus is a Neotropical genus of water scavenger beetle in the family Hydrophilidae represented by nine described species known from the Guiana Shield Region.

[2] It belongs in the subfamily Acidocerinae and contains nine described species from Brazil (Pará), Guyana, Suriname, and Venezuela.

[1][2] Small to medium-sized beetles (2.4–4.9 mm), smooth and shiny dorsally, orange-brown, reddish brown, or dark brown in coloration, with moderately long maxillary palps.

The elytral punctation ranges from shallow to strongly marked, forming impressed serial striae; all the species bear a well defined sutural stria.

[1][2] According to Girón and Short, "The habitats occupied by members of Primocerus range from forested pools to seepages".