346 E. L. Troxell — Palceolagus, an Extinct Rare. 



the condition most commonly seen in the species. The 

 next specimen shows the nnique double loop on the inter- 

 nal fold of P^ (fig. 13). 



Figures 14 and 15 show about the same state of wear ; 

 the latter is the more advanced, for M^ has lost the 

 crescent and P^ the antero-exterior fold which had been 

 confluent with its crescent. In the specimen shown in 

 figure 16, one should note the various results of w^ear: 

 P^ becomes much larger as the conical end disappears; 

 P^ is at its maximum width transverse ; P^ has lost its 

 crescent ; the inner fold of M^ is isolated to form a long 



Fig. 9—16. 



p^jT' 







Fig. 9.—Palceolagus haydeni. Cat. No. 12080, Y. P. M. Upper milk and 

 true molars. X 2. 



Fig. 10.— Palceolagus Jiaydeni. Cat. No. 12081, Y. P. M. Upper teeth of 

 young individual. X 2. 



Fig. 11. — Talceolagus haydeni. Cat. No. 10374, Y. P. M. Upper dentition 

 (except M^) of yoimg individual. X 2. 



Fig. 12. — Palceolagus haydeni. Cat. No. 10369, Y. P. M. Somewhat worn 

 upper dentition. X 2. 



Figs. 13-16.— Palceolagus haydeni, Cat. Nos. 12082, 10877, 12084, and 

 12083, Y. P. M. To show successively advancing stages of wear and reduc- 

 tion of lakes of upper molars and premolars. X 2. 



slender lake; M- shows the last sign of the crescent, 

 while M^ is reduced essentially to a simple cylinder. 



Other stages might be illustrated to show the final 

 elimination of all the foldings inside the outer boundary 

 of the tooth. 



In the following four views (figs. 17-20), of various 

 subspecies of P. haydeni, three show the milk teeth beside 

 the first true molar. In the first specimen (fig. 17) Dp^ 

 shows the prominent cusps and deep inf oldings which are 

 already much subdued in the next specimen {-^g. 18) ; 



