A new species of Apogon (Perciformes: Apogonidae) from the Saya de Malha Bank, Indian Ocean, with redescriptions of Apogon regani Whitley, 1951, A-gardineri Regan, 1908, and A-heraldi (Herre, 1943).

A new species of fish, Apogon quartus, known only from the Mascarene Plateau, is described. It is related to Apogon poecilopterus Cuvier in Cuvier and Valenciennes, 1828, Apogon carinatus Cuvier in Cuvier & Valenciennes, 1828, and Apogon queketti Gilchrist, 1903, recently treated by Con (1996) as members of the subgenus Jaydia Smith, 1961. Apogon quartus can be distinguished from these three species by having a single predorsal scale, 18 total (13 well developed) gill rakers on the first arch, and a single dark spot, perhaps appearing as an ocellus in life, on the body just behind the opercle flap. Six additional nominal species are added to the 10 valid (19 nominal) species treated by Con in Jaydia. Three of these names, Apogon argyrogaster Weber, 1909, formerly in Siphamia, Apogon melanopus Weber, 1911, and Apogon fuscomaculatus Allen & Morrison, 1996, are valid species. The holotype of Apogon heraldi (Herre, 1943) redescribed here, is a synonym of A. poecilopterus. Apogon fuscovatus Alien, 1985 was determined to be a synonym of A. melanopus by Alien & Morrison (1996) The other name, Apogon tchefouensis Fang, 1942, may be synonymous with one of the species Con treated but is not placed with certainty. Character overlaps between the subgenus Jaydia and other Apogon subgenera, particularly the largest subgenus Ostorhinchus Lacepede, 1802, are briefly examined. Virtually all derived characters of Jaydia grade into Ostorhinchus. Two rare species Apogon regani Whitley, 1951 and Apogon gardineri Regan, 1908 only known from the Mascarene Plateau are redescribed from new material. Both belong with the Apogon nigripinnis Cuvier in Cuvier and Valenciennes, 1828, complex of species.