PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON ll3(l):249-263. 2000. A new species of Apogon (Perciformes: Apogonidae) from the Say a de Malha Bank, Indian Ocean, with redescriptions of Apogon regani Whitley, 1951, A. gardineri Regan, 1908, and A. heraldi (Herre, 1943). Thomas H. Fraser W. Dexter Bender and Associates, Inc., 2052 Virginia Avenue, Fort Myers, Florida 33901, U.S.A. Abstract. — 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 & Va-lenciennes, 1828, and Apogon queketti Gilchrist, 1903, recently treated by Gon (1996) as members of the subgenus Jaydia Smith, 1961. Apogon quartus can be distinguished from these three species by having a single predorsal scale, 1 8 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 Gon in Jaydia. Three of these names, Apogon argyrogaster Weber, 1909, formerly in Siphamia, Apogon melanopus Weber, 1911, and Apo-gon fuscomaculatus Allen & Morrison, 1996, are valid species. The holotype of Apogon heraldi (Herre, 1943) redescribed here, is a synonym of A. poeci-lopterus. Apogon fuscovatus Allen, 1985 was determined to be a synonym of A. melanopus by Allen & Morrison (1996) The other name, Apogon tchefouen-sis Fang, 1942, may be synonymous with one of the species Gon 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 Cu-vier in Cuvier and Valenciennes, 1828, complex of species. The Russian vessel Vityaz made trawl genus Jaydia recently treated by Gon stations along the Saya de Malha Bank dur-(1996). The ten species of Jaydia have the ing 1989 collecting fishes. Two of these fourth dorsal spine longer than any other collections contained a new species and a dorsal spine, variable serrations on pre-specimen of Apogon regani Whitley, 1951. opercular edges, rounded or truncated cau-The new species was first identified as an dal fins, and some have bioluminescent or-Apogonichthys Bleeker, 1854c, based on the gans. Gon and Allen (1998) included an-mostly smooth preopercle edge and the other new species, Apogon photogaster in slightly rounded caudal fin. An examination Jaydia. A review of additional nominal spe-of internal and external characteristics led cies with possible relationships to the new to the conclusion that this specimen is an species yielded six names, Apogon argyr-Apogon Lacepede, 1802. Some characters ogaster Weber, 1909, (previously in Si-are held in common with species in the sub-phamia Weber, 1909, see Lachner 1953, p.