SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 65 



the upper and lower teeth of P. ctcrtideiis and, though both casts are 

 marked "type," there is probably some mistake involved, for the two can- 

 not be of the same individual, and in the original description of the species 

 only the mandibular dentition is mentioned ('91, 296). 



Localities. — The type oi P. australe was found on the banks of the Rio 

 Chico, for the other supposed species localities have not been given. No. 

 15,368 was collected by Mr. Hatcher at Killik Aike. 



• 



ProteroTherium principale Ameghino. 



(Plates X, Figs. 4, 5, 8, 11 ; XII, Figs, i, la.) 



DiadiapJiorus velox Lydekker [non Amegh.); Anales del Mus. de La 



Plata, T. II, 1893, p. 60. 

 Proterothenuin pnjicipale Aratgh..; Enum. Synopt, etc., 1894, p. 37. 

 Proterotheriiim divortium Amegh.; Ibid., p. 38. 



Proterotheritim dichotomum Amegh.; Anales del Mus. Nac. de Buenos 

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



Though nearly allied to P. mistrale, this appears to be a distinct species, 

 being not only larger than the latter, but also having certain peculiarities 

 of tooth pattern which appear to be of specific importance. P- has no 

 posterior conule and the postero-internal cusp (tetartocone) is very small 

 and imperfectly separated from the antero-internal (deuterocone), while in 

 p- this element is somewhat larger and more distinct, though decidedly 

 less so than in P. australe. The third upper molar has no hypocone, or 

 a very minute one, and the posterior ridge, formed by the cingulum, is 

 unusually low ; the protocone is very large, of pyramidal shape, and ex- 

 tends across nearly the entire internal face of the crown. 



In the mandible, the diastemata between the lateral incisor and the 

 canine and between the latter and the first premolar are very short. 



P. divortium (PI. X, figs. 4, 5), which was established upon portions of 

 the upper and lower jaws, appears to be only an individual of the present 

 species with slightly more slender mandible than is common. Of P. 

 dichotomttni (PI. X, fig. 8), the type is an isolated upper molar (m-) which 

 agrees quite closely in size and pattern with the corresponding tooth of 

 P. principale. 



In the subjoined table of measurements, No. 16 is a cast of the type; 

 No. 14 is a cast of a second and considerably older individual, an incom- 



