ケイ藻Cymbella leptoceros (Ehr.) Grun.の変異

概要

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Microphotographs of 365 individuals of Cymbella leptoceros collected in Mauritius were examined to determine their variations. They have been hitherto classified as var. elongata, forma curta, in variety, or form respectively, having been distinguished by the degree of protuberance on their venters, which belong to the taxon described from the type species. A considerable number of them are found impossible to be classified. These two varieties and the form should be defined as a synonym of their type species. Those having the shell protruded at rear end are usually called var. rostrata; however, intermediate shapes between var. rostrata and the typical species were discovered, which were apparently derived from the typical species, and accordingly should be defined as a synonym of the typical species. Those having a long shell (55μ in length) were formerly described as forma major, but, since observation by MEISTER (1912) had been made on individuals having a 50μ to 60μ long shelle, it is no longer necessary to classify them, and they should be defined as synonym of their typical species. Although those narrow individuals (i.e. 5μ to 10μ), have been described as var. angusta, I do not see any reason for classifying them. Materials that were obtained in Mauritius were measured to reveal the length 18.5μ to 32μ, the breadth 7μ to 9.5μ, ventral striae 8 to 12, and dorsal striae 8 to 11 in 10μ.
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