1893,] DR. C. J. FOBSTTH MAJOB, OS MIOC^SH SQUIRUELS. 183 



molars. This is a common form of inferior sciuromorph molar, as 

 Me meet \nth it, not only amongst most of the species of Sciunts, 

 but as well in Tamias, Spermophilus, and Airtomi/s. The cup is 

 bordered by the two anterior cusps, by t\\o posterior cusps, of 

 which the internal is generally less cleA'eloped or suppressed, by a 

 posterior heel, and sometimes by two secondary cusps between the 

 two pairs of principal cusps. Sometimes the basin-shaped appear- 

 ance becomes more evident still by the coalescing of all these cusps, 

 so that already in qidte unworn teeth, e. g. of the interesting Se. 

 everefti, Thomas (Plate IX. fig. 4), the rounded margin of the basin 

 appears perfectly even. 



In the Scmrus-vulgai'{s-tj]^e, the upper molars also present a 

 sort of basin, in order to receive the postero-external cusp of the 

 lower molars. This is the median valley, closed internally by the 

 largely developed internal cusp, and whose formation appeai-s to 

 be due to the partial atrophy of a transverse series of cusps, there 

 having remained only the internal one greatly developed, and 

 often, as in Sc. wlc/aris, a very small median cusp on the outer 

 side. In the Xerus-ty\)e, to be mentioned hereafter, we frequently 

 have the space of this median valley occupied by a transverse ridge, 

 which brings up to fi\e the number of these transAerse ridges in 

 the upper molars, with, between them, four narrow transverse 

 depressions instead of three, as is generally the case. 



The Sduropteri come near to the same type, presenting on the 

 whole a ti'ansitional stage between bunodontism and lophodontism, 

 with the cup-like shape of lower molars, to which corresponds the 

 formation of a median valley in the upper molars. In these last 

 we find, moreover, the anterior valley of the crown more fully 

 developed, than is the case in the members of the Scmms-vulfjaris- 

 type, and thus the molars of Scmropteri often present a more 

 elongate form. A characteristic feature of Sciuropterine molars is 

 a delicate wrinkling of the enamel of the valleys, and this, ac- 

 cording to the different species, extends more or less to the 

 cusps or crests, which thus appear crenate. 



Lower basin-shaped molars are met with as far back as the 

 Cernaysian fauna of Eeims, the lowest kno\\ n Eocene deposit in 

 Europe \ This is one of the reasons which makes me agree with 

 Schlosser^ in considering the fossils (Plesiadapis and Protoadapis), 

 described as Lemurids, to be Eodentia. The same conclusions, 

 and for the same reason, apply to Plesiestlionyx from the " Fanne 

 Ageienne " of Eeims % and to some specimens from the Eocene of 

 Egerkingen, doubtfully referred by Riitimeyer to Plesiadajns **. 



' Lemoine, "Etude cVensemble sur les dents des Mammiferes fossiles des 

 environs de Eeims," Bull. Soc. geol. de France, t. six. 1891, pi. x. figs. 64-fi8, 

 7(5-78. 



2 M. Schlosser, " TJeber die systematisclie Stellung der Gattnngen Pfe«iaf?ffpi.s, 

 Protoadapis, Pleitraspidothermm, and Orthaspidothermm" Neu. Jahrb, fiir 

 Mineralogie, Geologic und PahTontologie, 1892, Ed. ii. pp. 238-240. 



^ Lemoine, I. c. pi. x. fig. 32. 



■* L. Eiitimeyer, "Die Eocane Savigethievwelt vou Egerkingen," Abb. d. 

 scbweiz. paliiontol. Ges. vol, xviii. 1891, pp. 121-125, pi. fiii. figs. 16, 17. 



