TEETH OF THE MESOZOIC MAMMALS 23 



trigon reversing the pattern of lower molars, the accessory cusps being 

 on the outer side of the main or internal cusp, probably also derived 

 from the cingulum. Molars progressively styloid and piercing, often 

 with recurved tips. Lower incisors typically procumbent, spatulate, 

 p 3 and especially p 4 typically larger than m^ erect and piercing. 

 Postcanine teeth usually 11 (p i, in 7). 



1. Family Amphitheriidcc Owen. 



Lower and Upper Jurassic. Lower molars tuberculosectorial bifanged, 

 incisors more erect. Condyle low, coronoid broad, angle well rounded 

 below, sharply depressed. Postcanine teeth 9-12. Incisors more erect. 



Amphitherium, Lower Jurassic (Stonesfield Slate), England. Figs. 

 15, 17. 



Amphitylus, Lower Jurassic (Stonesfield Slate), England. Fig. 4 

 (No. 2). 



PeramiLs, Leptocladus, Upper Jurassic (Purbeck Beds), England. Figs. 

 18, 26. 



2. Family Amblotheriidce Osborn or Stylacodontidce Marsh. 



Upper Jurassic. Molars progressively styloid and piercing, finally 

 with single fang, canine with single fang. Coronoid more slender. 

 Angle small, continuous with lower contour of mandible. Mandible 

 graceful and slender. Incisors procumbent, spatulate. P 3 , p 4 larger 

 than m 1 . Postcanine teeth 11-12. 



1. Amblotherium (Upper molars = ? Peralestes) Upper Jurassic (Pur- 



beck Beds), England. Figs. 11, 23. 



2. Peraspalax, Upper Jurassic * (Purbeck Beds), England. Figs. 

 4 (No. 9), 22. 



3. Achyrodon, LTpper Jurassic* (Purbeck Beds), England. Fig. 24. 



4. Phascolestes, Upper Jurassic* (Como), Wyoming. Figs. 31-34. 

 Dri/olestes (probably a synonym of Phascolestes). 



5. Laodon, Upper Jurassic* (Como Beds), Wyoming. Fig. 30. 



6. Stylodon (Upper molars = ? Kurtodoti). Fig. 29. 



Stylacodon, Upper Jurassic * (Como), Wyoming (a synonym of 

 Stylodon?) 



7. Asthenodon, Upper Jurassic* (Como), Wyoming. Fig. 35. 



3. Family Paurodontidce Marsh. 



Upper Jurassic. Molars feebly tuberculo-sectorial, that is, with 

 accessory cusps poorly developed. Molars bifanged. Postcanine teeth 6. 

 Mandible very short and stout. 



*See note on page 22. 



