102 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



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]'](:. 4s. 1. M',1-1 -ill: .sV. ,s ,i,>>i'ii'nx (Stuttgart .Collection), a lower molar viewed from above ; lc, 

 posterior face; 16, external face, greatly enlarged. '2. .l/'V,Wr.\v. .-, (F J lii<i/iin/ii.i- -) ntinn-'i. from 

 above, o. riii<ii,inlti.i- minor, the lower molars viewed from above; 3n, external face of same 

 enlarged Oj diameters. 4. Ptilodus trovessartianus, lower molars viewed from above; 4((, ex- 

 ternal face of same ; ifl, internal tubercles ; eel, external tubercles. Original. 



KII:. 4'.i. Mi ,i/.vcr.iM!x, Laramie or Upper Cretaceous of North America. Probably an upper 

 molar viewed upon the wearing surface, enlarged two diameters. 



Fio. 50. , Left lower jaw of Cteiini-oi/uii .f rr/iliin, Marsh, from the Upper Jurassic or Basal 

 Cretaceous of North America, inner view, three times natural size ; b, Hight upper jaw of 

 C. potcns, inner view x 4. c, The same seen from below, a, First premolar, li, fourth preuiolar 

 as interpreted by Professor Marsh. After Marsh. 



Figs. 48-50. The molar tooth forms of the Multituberculate family Plagiauluci<ho. 



