190 DB. C. J. roilSYTH MAJOR OX MIOCEXi; SQUIERELS. [Feb. 2S, 



V. On the ]yrimitive Type of the Sciionne Molar, and of the 

 Eatherian Molar in rjencral. 



In surveying the A'arious modilications of the ^ciui'iue uiolav- 

 type, I refrained from entering into the question as to their relation 

 to the prevailing theory of trituberculisni. I proceed now to this 

 last part of my paper. 



The tritubercular theory has been worked out with admirable 

 acumen by Cope, Osborn, Schlosser, and lastly by Kiitimeyer and 

 8cott, and is so well known that I need not even gi\e a summary 

 of it. However, as 1 have to refer in the sequel to some less recent 

 papers bearing on the argument, I may be allowed to mention 

 them here as briefly as possible. 



In a Memoir, which may be regarded to contain the foundatious 

 of a I'eal compax'ative Odontography, Riitimeyer was led to consider 

 as fundamental type of the Ungulate molar the zygodont form, viz. 

 the upper molars formed by two transverse ridges, parting under 

 right angles from an outer wall (" Anssenivand"), with a transverse 

 valley dividing them, and two simple transverse ridges in the lower 

 molars \ 



fra Lagua JSaiita, Minas Geraes, Brasilieu. Med Udsigt over Gnavernes ind- 

 byrtes Slaegtskab" (Aftryk af "E Museo Lundii," Ivjobenliavn, 1887). I 

 regret not to have known this important publication before, but shall be obliged 

 to take it into full consicleratiou on the first op])ortunity if I succeed in over- 

 coming the difRculties presented by the language. Meanwhile, at the risk of 

 not having in every instance comjjletely grasped the author's meaning, I cannot 

 refrain here from a few obserAations. Winge presents (p. 110) the following 

 genealogical tree of the Rodentia : — 



Myoxidiv. Muridtv. 



Uipodidse. Hystricidic. Saccomyidee. 



\ / I 



Anonialiiridje. Sciuridsc. 



\ / 



Haplodontidte. 



Ischyromyidse. 



Leporida'. 



Pscudosciurus and Sciuroidcs are included as a distinct subfamily imder the 

 Anomaluridse, whicli last contain, moreover, besides Anomcdurtis (subf. Anoma- 

 liiriiii), the Tertiary Treclwm//» {Trcu/iomt/ini), Therido/iu/s, Issiodoruiiiys, Ar- 

 rhmoniys {Theridomi/ini), and the recent Pcdctes {Pcdc(ini). I do not in the 

 least deny the importance assigned to the masseter (in its relation to the 

 mechanical action of the teeth), and, as a consequence, to the shape of the 

 infraorbital foramen. However, the agreement in the molars of Sciuroides with 

 those of Sciuropterus horsficldi on the one side, and of Pscudoaciunis with 

 those of Scii'.ro2)terus pcarsoni (and to a lesser extent of AUoniys) ou the other, 

 is such that I do not think it justified to separate so widely these fossil forms 

 from the Pteromyiiice. Besides, amongst Sciuri/ice proper, Pnifoxeruf, my first 

 subgenus of Xerus, still presents, in the conformation of the infraorbital 

 foi'amen, some approach to the primitive condition. 



' L. Erlitimeyer, "Beitrage zur Kenntniss der fossilen Pferde und zur ver- 

 gleichenden Odontographie der Hufthiere iiberhaupt," Verb. d. naturf. Ges. in 

 Basel, iii. 1SG3, p. 5.:>8, gg. 



