A name Desmostylus mirabilis nov., is proposed for the remain recently acquired form a tributary of the Keton-gawa in Japanese Saghalin, which, the writer thinks, represents a species distinct form D., hesperus MARSH and D., japonicus TOKUNAGA and IWASAKI, the two well established species of the genus., It has a much larger skull with a narrower parietal region and smaller internoanterior column of the last upper premolar than the Oregon form and differs from D., japonicus in being provided with a broader M
2 and a smaller P
4 in the upper jaw and a broader M
2 in the lower., The columns of the lower M
2 are in the new species 7 in number instead of being 6 and those of the upper M
3 seem to be less slender.,
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