OF THE WHITE RIVER OLIGOCENE. 57 



comparable to those shown in Fig. 4 B (see table of measurements) 

 and are slender and compressed laterally. 



4. P^ is said to have a compressed laterally-grooved single root in 

 A. coarctafum. There are alveoli for two large roots in No. 12624 

 (Fig, 4 A) and the small Pi of the Hat Creek specimen is double- 

 rooted. 



5. The lower molars of A. coarctatum have the anterior tubercles 

 elevated above the posterior row. The same is true in both the Bear 

 Creek and Hat Creek specimens, but not more so than in some indi- 

 viduals of typical A. mortoni. 



6. Heels in lower molars with three tubercles, the third or poste- 

 rior median of which is said to be better developed than in A. mortoni, 

 especially on the last molar. Cope's figure shows the heel of m^ to 

 be as wide as the trigonid, with hypoconid and entoconid of the same 

 size, while in mg it is narrower, with three large cusps, the hypoconid 

 and entoconid of the same size and the hypoconulid very large. In 

 our Princeton specimen from Bear Creek the heels of both m^ and mg 

 are narrower than the trigonids, with the hypoconid the largest and 

 most prominent of the heel cusps, the other two being distinct but 

 much smaller (Fig. 4 A). In the Hat Creek specimen (No. 1481, 

 Am. Mus.) the heel of m, is less narrow transversely than in the 

 Princeton specimen, but the hypoconid is still the largest cusp, as it is 

 also in mg, where the entoconid on the right side is somewhat larger 

 than in the Princeton specimen and of about the same proportions as 

 in it on the opposite side. 



7. No internal cingulum is present on the molars of A. coarctatum 

 and the enamel is smooth. There are no internal cingula in the speci- 

 men from Bear Creek and the enamel is smooth on the triturating 

 surface of the crown and slightly rugose on the sides. In the Hat 

 Creek specimen it is practically smooth. 



8. Anterior border of coronoid sloping backward. Notch between 

 coronoid and condyle more deeply concave than in the Bear Creek 

 specimen, where the front edge of the coronoid rises vertically, as it 

 does also in No. 1481 from Hat Creek. 



9. Lower premolar crowns strongly compressed laterally, espe- 

 cially the anterior ones. None are preserved with our No. 12624, but 



