Seven specimens of natural hybrids of salmonid fishes were collected during 1971 to 1976 in the Nippara River, an upper tribute in the Tama River, Tokyo. In morphometric, meristic, and numerical characters as well as coloration, the natural hybrids showed intermediate character between the two native salmonids, Oncorhynchus masou and Salvelinus pluvius, which are only representative of salmonids in the drainage.Four specimens of artificially crossed hybrids between the same combination (O.masou×S.pluvius) were studied. Published records of natural salmonid hybrids as the cross between O.masou and S.leucomaenis, from Hokkaido, Sado Island, and unpublished record from Aomori Prefecture seem to support results of the cross of the same combination of species reported here from the Nippara River.
Gymnura japonica (Temminck et Schlegel, 1850) was described on the basis of specimens collected at Nagasaki.In the mean time G. bimaculata (Norman, 1925) was described on a specimen, 257 mm in total length, collected in the Chinese coast.In his brief description (18 lines) Norman pointed out characteristics of his new species as“it's tail is a little longer in comparison with known butterfly rays and there is a pair of oval bluish white ocelli at posterior side of spiracle.”Norman's species has long been regarded as valid by subsequent workers.Among them, some have either a pair of large white ocelli on disc or only one ocellus, or have a pair of large and small ocelli.Variation in pattern of white ocelli and in morphometric characters were studied on 24 individuals (specimens of Mus.Tokyo Univ. Fish., MTUF 22083-22106) from the East China Sea including young specimens.There is no valid reason for separation of two nominal species, and G.bimaculata should be regarded as a junior synonym of G.japonica.