The present paper, chiefly dealing with Rhizomys sumatrensis (Raffl.), is based on the examination of a series of specimens in the collections of the Rijksmuseum van Natuurlijke Historie, Leiden; Zoölogisch Museum, Amsterdam; British Museum (Natural History), London; Muséum d'Histoire Naturelle, Genève; Naturhistorisches Museum, Bern and the Collection of Mr. H. J. V. Sody, Amsterdam. To the following gentlemen I am indebted for the permission to study the specimens under their care: Prof. Dr F. Baumann and Dr W. Küenzi, Bern; Mr. A. C. V. van Bemmel, Amsterdam; Dr M. A. C. Hinton and Mr. R. W. Hayman, London; Dr G. C. A. Junge, Leiden; Prof. Dr P. Revilliod, Genève; Mr. H. J. V. Sody, Amsterdam. To Mr. M. A. Koekkoek, Rijksmuseum van Natuurlijke Historie, Leiden, my thanks are due for the carefully prepared drawings (textfigs. 1—4). For some unknown reason Raffles (1822, p. 258) gave the name Mus sumatrensis to a rodent, which was known from Malacca, but which at the time had not yet been recorded from Sumatra1). Temminck (1832, p. 7, pl. 1), who thought the name inappropriate, redescribed the species as 1) In the older literature the species has been mentioned from Sumatra by several authors, e.g., Lesson (1827, p. 265), Schlegel (1837, p. 235), M'Clelland (1842: fide Cantor 1846, p. 255), Murray (1866, p. 383), W. H. Flower & Garson (1884, p. 612), but they were probably misled by the name sumatrensis. The first positive evidence of the species occurring in Sumatra was given by Jentink (1887, p. 224). The species has also been said to occur in Borneo (Mohnicke 1883, p. 429; Tjeenk Willink 1905, pp. 264, 329; Van Balen 1914, p. 265), but these records have never been confirmed. Murray (1866, map 83) includes Java in the range of the Spalacidae, but he does