19(3 DK. f. J. roilSYXU MAJOR ox MIOCEIfE SQUIRRELS. [Feb. 28, 



A'. On the primitive Type of the Sciurine Molar, and of the 

 Eutherian Molar in ijencral. 



lu surveying the various modificatious of tlie yduriue luokr- 

 t\'pe, I refrained from entering into the question as to their relation 

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

 hist part of my paper. 



The trituberoular tlieory has been \\orked out with admirable 

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

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

 of it. However, as I 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, M'hieh may be regarded to contain the foundations 

 of a real comparative Odontography, Eiitimeyer was led to consider 

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

 the upper molars formed by t\\'o transverse ridges, parting under 

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

 valley di\iding them, and two simple transverse ridges in the lower 

 molars \ 



fi-a Lagua Santa, Minas Geraes, Brasilieu. Med Uclsigt over Guavenies ind- 

 byrtes Slaegtskab" (Afti-jk af "E Museo Liindii,'' Kjobeuhavn, 1887). I 

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

 to take it into full consideration on tlie first opjjortunity if I succeed in over- 

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

 not having in evei'y instance completely grasped the author's meaning, I canuot 

 refrain here from a few obser\ atious. Winge presents (p. 110) the following 

 genealogical tree of the Eodentia : — 



Myoxidaj. Muridii;. 



\. / 



Dipodidse. Hystricidaj. Sacoomyidse. 



\ / I 



Anomaluridffi. Sciuridie. 



\ , . / 



Haplodontida;. 



Ischyroinyida'. 



Leporida;. 



Pscudosciuriis and Scinroidiv are included as a distinct subfamily under the 

 Anomaluridae, which last contain, moreover, besides Aiwmcdurus (subf. Anoma- 

 turini), the Tertiary Trcchoiui/s {Trcchomyini), Thcridomijs, Isswdorom?/s, Ar- 

 thmumyi {Thcridomyini), and the recent Pcdctcs {Pcdcdni}. 1 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 Sciiiroidcs with 

 those of Scit(ro2}teriis horsficldi on the one side, and of Pseudosciurus with 

 those of Sciuro])tcrus pearsoni (and to a lesser extent oi Allomys) on the other, 

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

 from the Pteromyincs. Besides, amongst Sciiirlnce proper, Protoxerus, my first 

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

 foramen, some approach to the primitive condition. 



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

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

 Basel, iii. 1S(J3, p. 558, gg. 



