88 



AMERICAN MESOZOIC MAMMALIA 



molars prove to be entirely distinct in pattern. There were three erupted premolars and 

 apparently six erupted molars. Gathering together all the specimens which show the 

 premolars clearly (Fig. 38), one sees at once that the premolar distinction of the sup- 



H 



H' 



Fig. 38. Docoion. Diagrams of lower premolars in nine different specimens, 

 to show variability of Pj. B is younger than the others and is Marsh's Enna- 

 codon. H^ is a diagrammatic superior view showing the crowding of Pg.^ in H. 



posed genus Ennacodon is not that P2 is larger than Pi but that the homologue of P2 

 of the other forms is absent. With these changes in interpretation the differences for 

 which one must account are as follows : 



