74 



PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



Proterotherium cavum Ameghino. 



(Plates VIII, Figs. 1-3; IX, Figs. 11, iia; X, Figs. 15, i^a; XI, Figs, g-ga.) 



Proterotherium cavum Amegh.; Enum. sistem., etc., 1887, p. 19. 

 Diadiaphonis sanctce-crucis Lyddeker ; Anales del Museo de La Plata, 

 T. II, 1893, p. 60. 



This would appear to be the commonest and one of the most distinctly 

 marked of the Santa Cruz species of the genus. It is characterized by 

 small size, though in this respect there is much variability, and by the 

 comparative simplicity of the upper premolars, p- and - having a smaller 

 tetartocone, or postero-internal cusp, than in any of the preceding species. 

 In m- the postero-external cusp (metacone) is less reduced than in most 

 species of the genus, but narrower than the antero-external (paracone) 

 and the hypocone is small, but it appears to be constantly present. 



In the mandibular dentition, the canine is isolated by short, but distinct, 

 diastemata in front of and behind it, and px, though quite variable in size, 

 is generally larger than in P. intermedium and is implanted by two roots. 



In the table of measurements. No. 23 is a cast of an upper jaw in the 

 Ameghino collection labelled "co-type"; No. 24 is the cast of a mandible, 

 also labelled "co-type," but of a considerably smaller individual; No. 

 25 is a cast of an upper jaw of the same collection, while No. 26 is the 

 cast of the mandibular dentition of a fourth individual referred to this 

 species ; No. 9245 is the skull in the American Museum of Natural 

 History which is shown in Plates VIII, figs, i and \a; IX, figs. 11, \\a. 

 The identification of this skull is somewhat uncertain, as the teeth are so 

 worn that the pattern is almost obliterated. The measurements of the 

 type are taken from Ameghino {'89(5, 561). 





Measurements. 



















No. 







Type. 



No. 23. 



No. 25. 



9H5- 



Upper dentition, length i^-m-^ . 







.099 



•093 



.101 



I^, antero-posterior diameter 









.006 



.008 



.006 



" transverse diameter 









.005 



.008 



.0055 



Upper premolar-molar series, length . 







•07s 



.074 



.0685 



.076 



" premolar series, length . 









.040 



•0375 



•041 S 



Pl, length (i. e., antero-posterior diameter). 





.008 



.009 



.008 



.010 



" width {i. e., greatest transverse diameter) 





.007 



.007 



.009 



.007 



P^, length 



. 





.009 



.010 



.0085 



.010 



" width . . . ■ . 



, 





.008 



.011 



.012 



.0105 



