332 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



PREPOTHERIUM POTENS Ameghino. 



(Plates LX, Figs. 4-8 ; LXI.) 



Prepotherium potens Amegh. ; Rev. Argent, de Hist. Nat, T. I, 1891, 



P- 325- 

 Eucholczops titan Lydekker; Anales del Museo de La Plata, T. Ill, 1894, 



p. 98. 



This is much the largest known edentate of the Santa Cruz epoch and 

 is the commonest representative of the genus, though all of the specimens 

 yet obtained are lamentably imperfect and almost nothing is known of 

 the skull. In the Princeton collection are a number of individuals which 

 enable me to describe a considerable part of the skeleton, especially when 

 supplemented by the material in the Ameghino collection. 



Ameghino has described the teeth as follows: "The last upper molar 

 has a deep vertical groove on the posterior face ; diameter of m -, antero- 

 posterior 9 mm., transverse 16.5 mm. ; of - 6.5 x 12 mm." ('91, 325). "The 

 upper caniniform has a diameter of 9 mm. ; the diastema is 1 1 mm. long ; 

 the interdentary region of the palate between the caniniforms is 25 mm. 

 wide. The lower caniniform has a diameter of 7 mm. and the diastema 

 which follows it is 8 mm. long; the first upper molar has an antero- 

 posterior diameter of 10 and a transverse diameter of 15 mm. ; the last 

 lower molar has an antero-posterior diameter of 12 and a transverse 

 diameter of 15 mm. ; length of lower dentition 70 mm. ; height of mandi- 

 ble below penultimate molar 55 mm." ('94", 163-4). The Princeton col- 

 lection contains only two loose teeth associated with No. 15,521 ; one of 

 these, which may be the third upper tooth, measures ii-5x 18 mm., and 

 the other, which appears to be the second lower tooth, measures 9.5 

 x 13.5 mm. As appears from the measurements, the teeth are very much 

 compressed antero-posteriorly. 



The parts of the skeleton represented by the various individuals are ten 

 thoracic, four lumbar and three caudal vertebae, and most of the sacrum ; 

 two segments of the mesosternum and several ribs ; incomplete humerus, 

 ulna and radius, and much of the manus ; the greater part of the pelvis, 

 femur and tibia complete, and fibula nearly so, while the astragalus and 

 calcaneum are in the Ameghino collection. 



Although the vertebral formula is not known, it is evident that the 

 number of vertebrae was large, as is indicated by the great differences of 



