E. L. Troxell—Palcdolagus, an Extinct Hare. 341 



Po. Cope,2 Forsytli-Major,^ Matthew,* and others have 

 since pointed out additional differences: PalcBolagus 

 shows well developed postfrontal processes, the basicran- 

 ial angle very small, the brain relatively small and flat, 

 a less deep infolding of enamel on the internal side of the 

 upper molars, and the presence of a crescentic lake. In 

 all the Oligocene species the permanent lower teeth, when 

 little worn, show a small third lobe arising on the poster- 

 ior side of the second lobe near its summit; this, however, 

 soon disappears. It is an interesting fact that the two 

 lobes of the lower teeth are sometimes united only by 

 cement, having no enamel connection whatever (fig. 20). 



In the young, the anterior lobe of P3 is a distinct, nearly 

 isolated cone, l3ut later the indentations, especially that 



Fig. 2. — PalcBolagus haydeni. Cat. No, 10304, Y. P. M. Palatal view of 

 skull, to show small posterior nares, Pn, and anterior palatine foramina, 

 Apf. Nat. size. 



on the inner side, disappear, leaving the tooth as a single 

 column with a shallow groove down the outer side. The 

 anterior lobes take on two distinct types in the specimens 

 at hand, i. e., that of a cylinder, round, or flattened and 

 oval in cross-section. 



Forsyth-Major has pointed out that the anterior teeth, 

 both above and below, are more complicated than those 

 posterior; this, he says, is due to the loss of the first and 

 second molars of ancestral forms, thus throwing the addi- 

 tional burden on the anterior, terminal members of the 

 series. It is characteristic of the genus Palceolagus that 

 the posterior lobe of each lower tooth, after P3, should be 

 smaller than the anterior one. 



Additional features. — In comparing the fossil and 

 Recent skuUs (see figs. 1-3) of the family Leporidae in 

 the Marsh Collection, the following points have been 

 noted. 



- E. D. Cope, Eept. U. S. Geol. Survey Terr., 3, 870, 888, 1884. 



' C. J. Forsyth-Major, Trans. Linn. Soe. London (2), 7, 463-487, 1899. 



* W. D. Matthew, Bull. Am. Mus. Nat. Hist., vol. 16, 306-308, 1902. 



