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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Interatherium dentatum Ameghino. 
Interatherium dentatum Amegh. ; Enum. Synoptique, etc., p. 1 8, 1894; 
Segundo Censo, etc., p. 15 1, 1898 (listed). 
Approaching I. supermini in size. Distinguished by possessing an extra 
premolar in the upper jaw, that is to say five instead of four. The first 
two premolars are conic, the first or anterior being separated from the 
second. Complete upper dental series measures .041 (’94, 18). 
Interatherium senile (Ameghino). 
Icochilus senilus Amegh.; Enum. Synoptique, etc., p. 15, 1894; Segundo 
Censo, etc., p. 150, 1898 (listed). 
This species is of the size of /. extensus , but a little more robust. It 
is easily distinguished by the second lower premolar which is not bilobate 
but elliptical in contour and consequently without vertical groove either 
on the internal or the external face. The third and fourth lower premolars 
as well as the true molars are larger than in the other species. The sec- 
ond upper premolar is also of elliptical contour and without groove. 
There is a diastema of considerable length between the lower canine and 
the first premolar. Length of the seven lower molars .032 (’94, 15). 
Interatherium rotundatum (Ameghino). 
Icochilus rotundatus Amegh.; Contrib. al Conoc., etc., pp. 473-474, PI. 
15, figs. 1 5- 1 6 a, 1889; Enum. Synoptique, etc., p. 15, 1984; Segundo 
Censo, etc., p. 150, 1898 (listed). 
This species is separated by very marked characters. The skull is more 
prolonged anteriorly. I 1 very large, I- much smaller and I- still smaller. 
The upper incisors are closely crowded. P 1 is placed against the anterior 
part of P-. There is no upper canine, and there is a long diastema 
between the external upper incisor and the first premolar. Length, 
anterior part of I- to posterior part of M- .046 ; length of diastema 
between I- and P- .008 (’94, 15). 
Interatherium brevifrons Ameghino. 
Interatherium brevifrons Amegh.; Enum. Synoptique, etc., p. 18, 1894; 
Segundo Censo, etc., p. 15 1, 1898 (listed). 
Species much smaller in size than I rodens and with all the dentition 
in continuous series without diastemata. The anterior part of the skull 
