1893.] DR. C, J. FORSYTH MAJOR OX MIOCE?fE SQUIRRELS. 197 



Riitimeyer starts from the assumption that the primitive type 

 of Mammalian molars had a conical or cylindrical shape (" homce- 

 odont " type), ^^■hich simple form became complex in coiu'se of 

 time, SO that we must expect to find a more simple type of molars 

 the more we recede in time. Eiitimeyer's A'iews were supported 

 by the fact that, in several of the oldest deposits then known, of 

 Tertiary MammaUa Mere met with abundantly the Lophiodontida:', 

 show ing the zygodont molar in its typical form. 



Kowalevsky* held the same views as Eiitimeyer and pointed 

 out, besides, that a less simply constructed form of molars is met 

 ^vith in the older Tertiary, especially amongst "pximitive Ungulates" 

 (e.g. '■'■ Jlicrochcerus'')''. But whilst he did not enter upon the 

 possible relations bet\Aeen such complex sextnbercular forms and 

 the zygodont or lophodont type (as it Avas called later). Cope had 

 urged already, in 1S74, that a bunodont tooth was the ancestral 

 form of the modern placental molar, thus tacitly admitting that 

 the zygodont molar is a secondary, a derived form^ The various 

 modifications of ungulate molars were traced back by Cope to a 

 cjuadri tubercular type, and somewhat later he traced the sectorial 

 type of inferior molars to a quinquetubercular or tuberculosectorial 

 type*. 



The discovery of the Puerco, the oldest knoAAn Tertiary Mam- 

 malian fauna of America, gave opportunity for the recognition 

 by Cope of a still more primitive type of superior molar, the 

 tritubercular type, the great majority of the Puerco Mammals 

 having, according to Cope, their superior molars constructed after 

 this type^ In the latest review of the Puerco fauna it is stated 

 that almost all the Placentalia shoAv the tritubercular type in 

 their superior molars, as, out of 82 Placentalia, only four are 

 quadrituberculate. The quinqnetuberculate or tuberculosectorial 

 type of inferior molars is equally widely spread, although less 

 generally so, G4 out of 82 Placentalia possessing it". 



The farther development of the tritubercular theory in these 

 last years is treated of at length in all the recent Manuals, as the 

 \\'hole phylogeny of the Mammalia is directly connected with the 

 question. 



Not one palaeontologist \\ho has dealt with the argument has 



' W. Kowalevsky, " Monographie der Gattung Anthracothcriinn, Cuv.," 

 PalcTontographica, xxii. 1873, 1874, pp. 210, 2()3, 264. 



^ "Je ticfer wir in die Schiciiten driiigen, je iiltere Formen wir findeu, dcsto 

 complicirtere Gestalten taiichen iimiier :nif. . . . ; also kaun das als ein Wink 

 dieneii, wie weit wir noch von dei- ]}i-iniiiivf'n Form des Zalincf; sind" (/. c. 

 p. 230, note 1). 



^ E. D. Cope, "On tlie Homologies and Origin of tlie Tvpes of Molar Teeth 

 of Mammalia Educabilia," .Tonrnal Academy Nat. Seienee.s of I'iiiladelphia, 

 new series, vol. viii. pari 1 fPliiladelpliia, April 1874), pp. 71-89. 



' L.c. and E. D. Cope, "On the 'J'ridiboreulale Type of Molar Tooth in Iho 

 Mammalia," Tal. Bulletin, no. '.17, Proc. Amer. Philos. Soc.Dee. 7, 18S,1 ('puhl. 

 Jan. 2, 1884), p. 320. 



'' " On the Trituberculate Type &c.," /. c 



■' E. D. Cope, " Synopsis of Iho Vertebrate Fauna of the Piieruo Series," 

 Truusnet. American Philos. Soc, Ang. 1888, p. 200. 



