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Show 238 MR. OLDFIELD THOMAS ON THE MAMMALS [Nov. 3r its skull is very markedly larger, and its teeth even more so. That is, however, the species with which it seems most nearly allied. The presence of Rhipidomys roberii, like that of Neacomys, gives evidence of the affinity of the Cuyaba^ region of Matto Grosso with the eastern slopes of the Ancles, from which all the previous members of this group have hitherto come. In naming this distinct species after Mr. Robert I wish to make very special acknowledgment of the admirable work he has been doing in South America during the last three years. His collections, perfectly prepared in spite of all the difficulties incidental to a damp tropical climate and uncivilised surroundings, have revolutionised the material available in the British Museum for the study of the Mammals of Southern Brazil. Numbers of species, previously known to us only by the original descriptions or by a few unmeasured, discoloured, or otherwise imperfect specimens, are now represented by series of perfect skins with all the details incidental to good modern work. And again, the present collection, formed in a still more difficult country, links up in the centre his own Eastern Brazilian material with that obtained along the edges of the Andean chain by the late Mr. Perry 0. Simons. 19. NECTOMYS SQUAMIPES MATTENSIS, subsp. n. tf . 1005, 1019, 1025, 1037, 1050, 1203. $. 1031, 1033, 1048, 1109, 1131. External characters as in true squamipes and in garleppi; the latter also appears to grade into squamipes. Skull rather shorter and more rounded, less slender and elongated than in true squamipes. Nasals as usual narrow and elongate. Supraorbital edges with a marked raised bead, more developed than in squamipes, much more than in garleppi. Interparietal small, narrow antero-posteriorly, its anterior edge generally directly transverse. Palatal foramina long, widely open, with a slight angular constriction at the junction of their anterior and middle thirds. Opening of posterior nares wider the edge of the palate squarely transverse, the median pterygoid fossa broader anteriorly than posteriorly, its breadth in front greater than the length of m.1 Lateral pterygoid fossaa proportionally narrow and sharply pointed anteriorly. (In N. squamipes the median fossa is narrow anteriorly, broadening backwards, with a rounded anterior border.) Dimensions of the type, measured in the flesh :- Head and body 200 mm.; tail 200; hind foot (s. u.) 47 (extremes 44-47), (c. u.) 50 ; ear 24. Skull-greatest length 43 mm.; basilar length 34-6 ; zygomatic breadth 22'2 ; interorbital breadth 7; interparietal 3"4xll'5; palate length 20'4 ; palatal foramina 7-5 x 3-2 ; breadth of posterior palatal fossa anteriorly 3-8; length of upper molar series 6*3. |