1893.] DR. C. J. FORSYTH MAJOR Olf MIOCEXE SQUIRRELS. 197 



Eiitimeyer starts from the assumption that the primitive type 

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

 oclont" type), which simple form became complex in course of 

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

 the more we recede in time. Eiitinieyer's ^ieAvs were supported 

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

 Tertiary Mammaha were met with abundantly the Lophiodontid?e, 

 showing 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 

 with in the older Tertiary, especially amongst "primitive Ungulates " 

 (e. g. " Microchcerus ") ". But whilst he did not enter upon the 

 possible relations between such complex sextubercular forms and 

 the zygodont or lophodont type (as it Mas called later), Cope had 

 urged already, in 1874, 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 

 qnadritubercular 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 known Tertiary Mam- 

 malian faiuia 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, accordiiig to Cope, their superior molars constructed after 

 this type". In the latest revie\v of the Puerco fauna it is stated 

 that almost all the Placentalia show the tritubercular type in 

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

 quadrituberculate. The quinquetuberculate or tuberculosectorial 

 type of inferior molars is equally widely spread, although less 

 generally so, 64 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 

 whole phylogeny of the Mammalia is directly connected with the 

 question. 



Not one palaeontologist who has dealt with the argimient has 



^ W. Kowalevsky, " Monograpbie der Gattung Anthracotherium, Ciiv.," 

 Palffiontographica, xxii. 1873, 1874, pp. 210, 263, 264. 



^ " Je tiefer wir in die Schicbten driugen, je altere Pormen wir finden, desto 

 complicirtere Gestalten tauchen i)umer auf. . . . ; also kann das als ein Wink 

 dienen, wis weit wir nocb von der primitiven Form des Zahnes sind " {I. c. 

 p. 230, note 1). 



^ E. D. Cope, " On tbe Homologies and Origin of tbe Types of Molar Teetb 

 of Mammalia Educabilia," Journal Academy Nat. Sciences of Pbiladelpbia, 

 new series, vol. viii. part 1 (Pbiladelpbia, April 1874), pp. 71-89. 



' L.c. and E. D. Cope, "On tbe Trituberculate Type of Molar Tootb in tbe 

 Mammalia," Pal. Bulletin, no. 97, Proc. Amer. Pbilos. Soc, Dec. 7, 1883 (publ. 

 Jan. 2, 1884), p. 326. 



•5 " On tbe Trituberculate Type &c.," I. v. 



■^ E. D. Cope, "Synopsis of tbe Vertebrate Fauna of tbe Puerco Series," 

 Transact. American Pbilos. Soc, Aug. 1888, p. 299. 



