The pomacentrid fish genus Chromis is represented in Japan and Taiwan by the following20species: C.albomaculata Kamohara, C.alleni sp.nov., C.analis (Cuvier), C.atripectoralis Welander et Schultz (often confused with C.caerulea), C.atripes Fowler et Bean, C.caerulea Cuvier, C.chrysura (Bliss) (C.lepidostethicus (Fowler), C.westalli (Whitley) and C.isharae (Schmidt) are junior synonyms), C.elerae Fowler et Bean (recorded for the first time from Taiwan;not yet known from Japanese waters);C.flavomaculata Kamohara (C.kennensis (Whitley) is a junior synonym), C.fumea (Tanaka) (described as a Pomacentrus, here revealed as a Chromis;C.caudofasciata Shen et Chen is a junior synonym), C.lepidolepis Bleeker, C.leucura Gilbert (first record from Japan);C.margaritifer Fowler (often misidentified as C.dimidiata;C.bicolor (Macleay) is a homonym), C.mirationis Tanaka (C.fraenatus Araga et Yoshino is both a synonym and a homonym), C.notata (Temminck et Schlegel) (C.villadolidi Jordan et Tanaka and C.miyakeensis Moyer et Ida are synonyms), C.ovatiformis Fowler, C.ternatensis (Bleeker), C.vanderbilti (Fowler), C.weberi Fowler et Bean (often misidentified as C.xanthochir), and C.xanthura (Bleeker).C.alleni is described from specimens from the Ryukyus, Izu Islands, Taiwan, and Ogasawara Islands.It is dark yellowbrown, abruptly whitish on caudal peduncle and fin, with a large blackish spot at pectoral base.Allied to other small bicolored Chromis with produced filamentous caudal lobes, it differs in having modally 13 dorsal soft rays, 17 pectoral rays, and 15 or 16 tubed lateral-line scales.