This slightly papillated, sunken area, along with the papillated posteromedian patch, forms a slightly papillose triangular patch on the chin,as shown in Lin’s figure of R. mutabilis. Examination of the specimens from throughout it’s the known distributions showed that this posteromedian patch is rudimentary or absent in small-sized specimens (Fig. 3C). This does not disagree with the original description of R. mutabilis. Comparison of morphometric data provided in their original descriptions indicated that R. mutabilis and R. luxiensis differ in the caudal-peduncle length and interorbital width (see Table 2), but these differences are not so surprising given only six type specimens for these two species. The index values for these two characters in the original description for the type material of R. mutabilis are not distinct from those calculated from measurements taken for the type material of R. luxiensis (see Table 2). Also, no differences are found between these two species in meristic counts except for lateral-line scales. The difference in lateral-line scales can be explained by utilizing different methods to count them. Those on the caudal-fin base were included by Lin (1933) in lateral line scales, but not included by Wu et al. (1977). These findings lead us to conclude that R. luxiensis is probably a junior synonym of R. mutabilis (Lin 1933).