yS PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



The perissodactyl similarity of the molar pattern is produced by the 

 slight backward displacement of the posterior conule, bringing it into 

 closer connection with the hypocone and opening the valley internally. 

 When abraded, the tooth shows two transverse crests, which though in- 

 complete, suggest those of Mesohippus or Anchitherium. The hypocone 

 is small in m- and absent in m-. In the latter, the posterior crest formed 

 by the elevated cingulum does not reach the external wall and thus the 

 longitudinal valley opens backward in quite peculiar fashion. On the 

 outer wall of the molars the mesostyle is unusually low and the external 

 cusps have but a slight concavity. 



Measurements. 



P-^, length («'. ^., ant. -post, diam.) . .on M^, width 0165 



" width (/.?., greatest trans, diam.) . 013 M-, length 014 



pi-, length 012 " width 017 



" width . . . . . .015 M-^, length 012 



Upper molar series, length . . .035 " width ..... .017 



Mi, length 012 



Locality. — The specimens in the Ameghino collection were found at 

 Kar Aike. 



Proterotherium politum Ameghino. 



(Plate IX, Fig. 10.) 



Proterothermm politum Amegh. ; Anales del Mus. Nac. de Buenos Aires, 

 Ser. 3, T. Ill, p. 152. 

 This supposed species, represented by a single tooth, is quite indeter- 

 minable. No locality is given for the type. 



Proterotherium dodgei sp. nov. 



(Plates IX, Figs, i, \a, 5, 6 ; XI, Figs. 1-8 ; XII, Fig. 2.) 



Among the material collected by Mr. Hatcher at Lake Pueyrredon is a 

 species of Proterotherittm, represented by two very fragmentary skeletons, 

 which differs in significant details from any of the species previously 

 described. There is reason to believe that the Santa Cruz beds displayed 

 at Lake Pueyrredon represent a ^mewhat lower and older horizon than 

 the beds along the Atlantic coast and it is therefore probable that we have 

 to do here with actual specific mutations and not with mere contempo- 

 rary variations. 



The type of P. dodgei is a specimen (No. 15,107) consisting of the 



