110 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



ing Acmeodon, its outer wall looking as if it had been plastically de- 

 formed, by pressing the apex outward. Except for details in the 

 generic diagnosis or evident from the measurements, the lower molars 

 so closely resemble those of Didelphodus absarokae, described by 

 Matthew (1918), that further description of them is not necessary. 



There is a s;ingle left M^, U.S.N.M. no. 9554, from the Gidley 

 Quarry, that may belong to this species, although it differs more 

 markedly from Didelphodus absarokae than do the lower molars. It 

 is remarkably short and wide, or extremely transverse, and further 

 differs from Didelphodus in the great extension of the parastyle spur, 

 the slightly more external position of paracone and metacone, and the 

 vestigial character of the metaconule. It resembles Didelphodus in 

 other respects, such as the emarginate outer border, shelf-like meta- 



a 



Figure 12.— Oelastops parens Simpson, U.S.N.M. no. 

 6148: Right lower jaw, external view. Twice natural 

 size. 



Figure Vi.—Gelastops parens Simpson; 

 a, Crown view of right lower teeth 

 and alveoli, U.S.N.M. no. 9601; b, 

 internal view of right lower jaw, U.S. 

 N.M. no. 9850. Twice natural size. 



stylar extension, connate bases of paracone and metacone, and entire 

 absence of hypocone or of anterior or posterior cingula. The trans- 

 verse extension and the reduction of the metaconule are, furthermore, 

 Didelphodus-like but here more extreme and the nonmarginal position 

 of paracone and metacone are also Didelphodus-like but less pronounced. 



Table 22. — Measurements of individual specimens of Gelastops parous. 



