[1] Chilton's second species, P. propinquus was described in 1907 from a single specimen collected near the summit of Mount Anglem on Stewart Island / Rakiura.

Chilton originally thought this specimen was a male, but later realised that it was in fact female.

[2] It is a coastal freshwater species, only occurring further inland near Hamilton on the Waikato River system.

[2] Few scientists have worked on the genus Phreatogammarus after Charles Chilton, and it was not until 2003 that a fourth species was described.

M. A. Chapman, in a revision of the genus, established a new species, P. waipoua for populations of Phreatogammarus living in two forests in Northland Region.