Proj. 0. C. Marsh — American Jurassic Mammals. 247 



distinct traces of wear on their outer surfaces. The first true molar 

 is placed obliquely, as in the previous specimen, and has been sub- 

 jected to much attrition. The last true molar was situated lower 

 than the first, and was also oblique. In Ctenacodon serratus, the two 

 lower molars are nearly on a level. The present specimen shows 

 that the angle of the jaw was strongly inflected, and there was like- 

 wise a ridge on the opposite outer margin. The coronoid process 

 had its front border more nearly perpendicular than in Ctenacodon 

 serratus. There is no trace of a mylohyoid groove. 



The known specimens of this species are from the Upper Jurassic 

 deposits of Wyoming. 



EXPLAJSTATIOlSr OF PLATES VI. and VII. 



PLATE VI. 



Fig. 1. Left upper jaw of ^^^rfoM ^«<icej[?s, Marsh; outer view. 



,, 2. The same specimen ; seen from below. 



,, 3. Left upper jaw of same species ; inner view. 



,, 4. The same specimen ; seen from below. 



,, 5. Left upper jaw of same species ; outer view. 



,, 6. The same specimen ; seen from below. 



„ 7. Eight premaxillary of Allodon fortis, Marsh; outer view. 



,, 8. The same specimen ; seen from below. 



,, 9. The same specimen ; seen from in front. 



., 10. The same specimen ; inner view. 



„ 11. Portion of left upper jaw of ^^fo(?ow/or<isy outer view. 



,, 12. The same specimen ; seen from below. 



,, 13. The same specimen ; inner view. 



„ 14. howei incisov of Allodon fords ; side view. 



,, 15. The same incisor ; seen from in front. 

 a, last incisor ; a", second premolar ; b, fourth premolar ; b', third premolar ; 



c, second tiue molar; c, first molar ;/, antorbital foramen; ?«, malar arch ; 



s, suture with maxillary. 

 Figures 1-4 are four times natural size ; 5 and 6, six times natural size ; 7-15, 



three times natural size. 



PLATE VII. 



Fig. 1. Eight lower jaw of Ctenacodon serratus, Marsh; outer view. 



The small figure is natural size, and the larger one is magnified four diameters. 



Fig. 2. B.ightwp^er ja,\f oi Ctenacodon potens,Ma.Tsh.; inner view. 



3. The same jaw ; seen from below. 



4. Left lower jaw of Ctenacodon serratus; inner view. 



5. Incisor, probably of same species ; seen from in front. 



6. The same incisor ; seen from the side. 



7. Left lower jaw of Gttnacidon poteois ; outer view. 



8. The same jaw ; inner view. 



9. The same jaw ; front view, with its fellow restored in place. 



In Figures 2 and 3, a, first premolar; J, fourth premolar; c, second molar ; 



m, malar arch. In the lower jaws, a, incisor ; b, condyle ; c, coronoid process ; 



m, molar ; r, root of incisor ; s, symphyseal surface. 

 Figures 2, 3, 5 and 6, are four times natural size, and Figures 4, 7, 8 and 9, are 



three times natnral size. 



{To be continued.) 



