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Show 706 DR. C. I. YORSYTH MAJOR ON THE [Junel, old row in some genera, \h., Allomys1 and Pseudosclurus; the pattern of molars of the last named he considers to be the most primitive amongst known Bodentia 2. He places Pseudosclurus in the Anomaluridae, from which family he derives the Hvstricidae and Dipodidae, and from the latter the Myoxidae and Muridae3. I have many years ago4, and so had Hensel5 before me, drawn attention to the great resemblance of the molars of Pseudosclurus to those of Ungulates ; they were compared by me in the first line with the molars of " Hyracotherlum siderolithlcurn." With regard to Allomys I refer to a more recent paper of mine °. Besides, I wish to draw attention to a fact, which will be more fully considered by m e in another place, viz., that amongst the Sciuropteri we equally meet with traces of these ancient outer cusps, namely in S. pearsonl 7, and especially in S. xanthlpes, Milne-Edw., of which a less worn dentition than that figured by Milne- Edwards a lies before m e (B.M. no. 95. 7. 5. 1). These ancient cusps are further met with in Aplodontla, in whose premolar and molars the middle outer cusp in upper, and the middle inner cusp in lower molars, Winge's 2, are the most conspicuous of the three. Coues considered Aplodontla to be a very primitive genus, adducing for one of his reasons that the molars are of the most simple type9. There is no doubt that this genus is a very low form of Bodentia 10, as shown by the skull-in spite of its highly fossorial specialization-and by the structure of the molars ; but not for the reason adduced by Coues; for in an unworn condition, as figured by Schlosser ", they are shown to be of a complicated type. W e have next to face the question, what becomes of these ancient outer cusps in the upper molars of Mammals generally ? Years ago I tried to show that the vertical ridges on the outer side of the molars of modern Ungulates are not the unimportant parts which they are generally held to be 12; and Winge has since identified them as the homologues of the outer series (1, 2, 3) of Insectivora and Polyprotodontia13. In proportion as the next following inner cusps, 4 and 5, increase in size and at the same time apparently move outwards, the outer cusps decrease and either become fused with 4 and 5, or persist between them in the 1 'Gnavere fra Lagoa Santa, etc.,' p. 114. 2 lb. p. 116. 3 lb. p. 110 etc. 4 Paheontographiea, vol. xxii. 1873, p. 76. 5 Zeitschr. d. deutsch. geol. Ges. viii. 1856, p. 664. c " O n some Miocene Squirrels etc.," P. Z. S. 1893, pp. 192, 193. 7 lb. pl. viii. fig. 20. a ' Rech. p. servir a l'Hist. nat. des Mammiferes,' Paris, 1868-74, p. 171, pl. 1 5 A. fig. 3. 0 E. Coues and J. A. Allen, "Monographs of North American Rodentia," Report Un. St. Geol. Survey of the Territories, Washington, 1877, p. 555. 10 See Winge, ' Gnavere fra Lagoa Santa,' pp. 108, 110, 115. 11 M . Schlosser, " Die Nager des europaisjhen Tertiiirs," Palajontographica, xxxi. 1884, p. 106 (124). 12 >< Nageriiberreste aus Bohnerzen Suddeutscblands und der Schweiz," Palai-ontographica, xxii., 1873. 13 " O m Pattedyrenes Tandskifte etc.," I.e. pl. iii. |
