Three species of the serranid genusPlectranthiasoccur at Mauritius:Plectranthias winniensis(Tyler, 1966).P. inermisRandall, 1980 andP. pelicieriRandall and Shimizu, 1994. A recently collected specimen ofP. inermisprovided new data on intraspecific variation of what were previously supposed to be diagnostic characters for this species. Although this new specimen has a complete lateral line and 20 dorsal-fin rays, compared with an incomplete lateral line and 16–18 rays previously reported forP. inermis, all of the other diagnostic features (preopercle, interopercle and subopercle smooth; dorsal fin divided almost to the base between spinous and soft-rayed parts; pectoral-fin rays 13. all unbranched; one row of scales between lateral line and base of middle dorsal fin spines and one row of scales between dorsal-fin origin and lateral line; snout, preorbital, maxilla, lower jaw and interorbital area naked, cheek with 5 oblique rows of scales) agree withP. inermis.New data for all three species ofPlectranthiasknown from Mauritius are presented. Colour photographs of the two species that have not previously been illustrated in colour (P. inermisandP. winniensis) are included.