1893.] DR. c. J. roRSYTir major oy miocene squirrels. 1*^3 



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

 we meet with, it, not only amongst most of the species of Scit(n(s, 

 but as well in Tamias, Sperrno2^IiilHS, and Arctomi/s. The cup is 

 bordered by the t\\o antei'ior cusps, by Uvo posterior cusps, of 

 which the internal is generally less developed or suppressed, by a 

 posterior heel, and sometimes by two secondary cusps between the 

 two pairs of pi'incipal cusps. Sometimes the basin-shaped ajjpear- 

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

 so that already in quite unworn teeth, c. (j. of the interesting Sc. 

 evereili, Thomas (Plate IX. fig. 4). the rou)ided margin of the basin 

 appears perfectly even. 



In the 8cinrus-vnl(jarls-\\]}e. the upper molars also ^^resent 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 appears 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 Be. indr/aris, a very small median cusp on the outer 

 side. In the J(?)-u5-type, to be mentioned hereafter, we frequently 

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

 which brings up to five the number of these trajisverse ridges in 

 the upper molars, with, between them, four narrow trans^'erse 

 depressions instead of three, as is generally the case. 



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

 Avhole a transitional 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 Sciurus-vulgaris- 

 type, and thus the molars of Sciuropieri 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 

 CVmaysian fauna of l^eiins, the lowest known Eocene deposit in 

 Europe '. This is one of the reasons Mhich makes me agree with 

 Schlosser'- in considering the fossils (Pleslculapis and Protoadapis), 

 describfKl as Lemia-ids, to be Rodentia. The same conclusions, 

 and for the same reason, apply to Plmcsihontia; from the " Faune 

 Agc'ienne" of Eeims ', and to some specimens from the Eocene of 

 Egerkingen, doubtfully referred by Iliitimeyer to Plrsiadapis \ 



' Loinoiiie, "Etude d'ensenible sur los dents des Maininiferea fossiles de3 

 environs de Reims," Bull. Soc. geol. do Franco, t. xix. lft*.)l, pi. x. figs. (54 -()8, 

 7(V-7ft. 



' M, Schlosser, " Ueber die systematiselieStellungderOaltungen P?<'6'/a(7fl'/)/.s, 

 Protoadapis, I'lmraapidolhcriiiiii, and Or/haspidnfhcrium" Neu. Jalirb. I'tir 

 Mineralogie, Geologic und Palioutologie, IS'.t'J, Bd. ii. pp. 238-240. 



^ Lenioine, I. c. pl. x. fig. .'52. 



' L. Riitinieyer, " Dio Eociine Siiugetliierwolt vou Egerkiugen," Abli, d. 

 scliweiz. paliiontol. Ops. vol. wiii. \''^'-^\, pi). 121 12.'. pl. viii. figs. Id, 17. 



