Among the specimens of Leptomysim (Crustacea, Mysidacea) collected from the northern part of the South China Sea by the Institute of Oceanology, Academia Siniea, Leptomysis xenops Tattersall and a closely related form were found by the authors. While studying on the morphological characteristics of these two species and their allies in the Tribe Leptomysini, we found that there are two natural groups of species previously ascribed to the genus Leptomysis G. O. Sars. The first group includes the type species of the genus and other 8 known species, viz. Leptomysis gracilis (G. O. Sars. 1864), L. lingvura (G. O. Sars, 1866), L. sardica G. O. Sars, 1877, L. mediterranea G O. Sars, 1877, L. capensis Illig, 1906. L. megalops Zimmer, 1915, L. australiensis Tattersall, 1927. L. peresi Bacescu, 1966, and L. burgii Bacescu, 1966, of which the cornea of the compound eye is normal——with numerous small facelets of equal size, the telson is usually armed with 2 or 3 pairs of larger apical spines; while in species of the second group, in which L. apiops apgops G. O. Sars, 1877, L. apiops banyulensis Bacescu, 1966, L. xenops Tattersall. 1922 and the new species described in this paper are included, the cornea consists of two parts, the anterior part with small and normal faeelets, but of the posterior part, the facelets are very unique, being larger and much elong ted to form a “bauquet”-shaped process. These differences showed that the two groups are heterogenous and belongs actually to two distinct genera. In order to receive the last 4 forms, a new genus, Paraleptomysis gen. nov. is established, and an account of the new genus and Chinese species is given in this paper. The type materials of the new species, P. sinensis sp. nov. are kept in the Institute of Oceanology, Academia Sinica (Qingdao). Among the specimens of Leptomysim (Crustacea, Mysidacea) collected from the northern part of the South China Sea by the Institute of Oceanology, Academia Siniea, Leptomysis xenops Tattersall and a closely related form were found by the authors. While studying on the morphological characteristics of these two species and their allies in the Tribe Leptomysini, we found that there are two natural groups of species previously ascribed to the genus Leptomysis GO Sars. The first group includes the type species of the genus and other 8 known species, viz. Leptomysis gracilis (GO Sars. 1864), L. lingvura (GO Sars, 1866), L. sardica GO Sars, 1877, L. mediterranea G. O. Sars, 1877, L. capensis Illig, 1906. L. megalops Zimmer, 1915, L . australiensis Tattersall, 1927. L. peresi Bacescu, 1966, and L. burgii Bacescu, 1966, of which the cornea of ​​the compound eye is normal - with numerous small facelets of equal size, the telson is usually armed with 2 or 3 pairs of larger apical spines ; while in species of the second group, in which L. apiops apgops GO Sars, 1877, L. apiops banyulensis Bacescu, 1966, L. xenops Tattersall. 1922 and the new species described in this paper are included, the cornea consists of two parts, the anterior part with small and normal faeelets, but of the posterior part, the facelets are very unique, being larger and much elong ted to form a “bauquet” -shaped process. These differences showed that the two groups are heterogenous and belongs actually to two distinct genera. In order to receive the last 4 forms, a new genus, Paraleptomysis gen. nov. is established, and an account of the new genus and Chinese species is given in this paper. The type materials of the new species, P. sinensis sp. nov. are kept in the Institute of Oceanology, Academia Sinica (Qingdao).