Two types of Semisulcospira in Kamo river was discriminated by means of electrophoresis and comparison was made on forms of adults and embryonic shells using samples collected at four stations along this river. The results of electrophoresis showed that they belong to different species without random crossing though the shape of adults that were continuously changing. The A-type was distributed to the upper stream, and the B-type to the midstream. At a sympatric station, Takahashi, the B-type adults often had a tendency to lose ribs and decrease number of whorls, and were similar to the A-type. The discrimination of these two types was unclear only by adult or embryonic shell morphology, but it was possible when size and number of embryonic shell were taken into account. But, size and number of embryonic shell of the A-type from the upper stream, Kibune, were close to those of the B-type, and a discrimination of the two species was difficult between different stations. The A-type had small embryos, except Kibune, but a good percentage of embryonic shells had ribs being different from the description of S. libertina. Although the A-type was different from topotypic S. libertina in genetical and morphological of embryonic shells, it was unknown if these variations are interspecific differences or geographic variations. The B-type was to be identified as S. reiniana that was described on the specimens from the Lake Biwa or Uji river.
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