Prognathodes dichrous is found in the southeastern Atlantic Ocean where it is endemic to the waters around the British Overseas Territories of Ascension and Saint Helena islands.

[1] Prognathodes dichrous is a species of deeper water, normally found between 12 and 35 metres (39 and 115 ft) but ar Hummock Point it can be seen in water as shallow as 1 metre (3.3 ft).

[2] It is normally encountered in pairs, although shoals have also been recorded, which browse on benthic invertebrates over rocky areas.

[2] Prognathodes dichrous was first formally described in 1869 by the German-born British zoologist Albert Günther (1830–1914) with the type locality given as St Helena.

[3] Its closest relative appears to be the rather similar Prognathodes obliquus which is endemic to St Paul Rocks off Brazil.