io6 
PATAGONIAN EXPEDITIONS ! PALAEONTOLOGY. 
The others are placed on the sides with the principal diameter in the direc- 
tion of the dental series. The anterior part of the crown is a little broader 
than the root, with the apex bilobate by an internal groove which gradually 
disappears on wear, but the canine, which has not the groove, has an 
acutely conical crown. P T , which is separated from the canine by a short 
diastema, is similarly shaped but implanted vertically. P x is low and 
bilobate by two opposite grooves, each lobe elliptico-triangular, and the 
two of almost equal size, the base divided into two separate and quite 
long roots. P ¥ and P T and M x and M x are composed of two elliptico- 
triangular, almost equal prisms separated by two opposite grooves which 
extend to the completely open base. Each prism is a little narrower on 
the inner than on the outer side, without reentering folds or salient ridges. 
M3 is composed of three unequal subprismatic parts, the median twice as 
large as the anterior and the last one half smaller but on the inner side 
fused with the second. Length of space occupied by the seven upper 
molars .021 ; length of space occupied by the seven lower molars .023 
(’89, 467-468). Founded on an immature individual with the milk denti- 
tion. A photograph by Professor Scott of the anterior part of the skull 
referred to above shows very clearly by the texture of the bone that the 
individual is far from adult. 
Interatherium supernum Ameghino. 
Interatherium supermini Amegh. ; Enumeracion Sistematica, etc., p. 15, 
1887 ; Contrib. al Conoc., etc., pp. 468-469, PI. 15, figs. 17-19$, 
1889 ; Enurn. Synoptique, etc., p. 18, 1894 (listed) ; Segundo Censo, 
etc., p. 1 5 1 , 1898 (listed). 
This species is one-third larger than I. rodens , from which it is easily 
distinguished by the molars which are shorter and broader, the interme- 
diate molars being of almost equal length and width, while in /. rodens 
the antero-posterior diameter of the crown always considerably exceeds 
the breadth. Further, in the premolars, the internal reentering fold is 
deeper than in I. rodens but is not extended into a vertical groove, whence 
the inner side is not bilobate but of vertically convex surface and notably 
narrower than the external surface. P- differs from P- and P- in being 
more compressed, with crown much longer than wide, resembling the cor- 
responding tooth in /. rodens , but without the internal groove of the lat- 
ter. All the upper premolars and molars have the same antero-external 
