A platycephalid fish, Onigocia grandisquama ( Regan, 1908 ) is rediagnosed based on 52 specimens, including the holo-type, from the Indo-West Pacific. Geographic variation in the species was recognized in the number of pectoral-fin rays, the first example of such variation in fin ray counts in the Platycephalidae. The species displays wide intraspecific variation in the numbers of lachrymal, preocular, suborbital, and pterotic spines, with values for the first two overlapping with those of the very similar Onigocia spinosa (Temminck and Schlegel, 1843), making it difficult to separate the two. Onigocia grandisquama can be distinguished from O. spinosa, as well as from Onigocia macrocephala (Weber, 1913) and Onigocia macrolepis (Bleeker, 1854), which share with O. grandisquama an ocular flap on the posterior part of the eye, in lacking spines on the inner, middle, and/or outer ridges of the lachrymal. The generally greater number of pterotic spines also helps to separate O. grandisquama from its three congeners.
I express my sincere thanks to M. Gomon (NMV), who critically read a draft manuscript of this paper. I am deeply indebted to M. Aizawa (formerly Coastal Branch of CMNH; now Biological Laboratory, Imperial Household); M. Hammer, G. Dally, and R. Williams (NTM); A. Graham (CSIRO); T. Iwamoto and D. Catania (CAS); J. Johnson (QM); H. Larson (formerly NTM); K. Matsuura and G. Shinohara (NSMT); M. McGrouther (AMS); J. Maclaine (BMNH); G. Moore and S. Morrison (WAM); M. J. P. Oijen and J. Egmond (RMNH); P. Pruvost (MNHN); M. Sakashita (Nago, Okinawa); P. Sirimontaporn (NICA); A. Suzumoto (BPBM); R. Vonk and Praagman (ZMA); J. Williams and L. Knapp (USNM); and all other staff of the fish sections of the aforementioned museums for making specimens available. This study was partly supported by JSPS (Japan Society for the Promotion of Science) KAKENH Grant Number 16K07472 and JSPS Core-to-Core Program—Research and Education Network on Southeast Asian Coastal Ecosystems.