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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Intermediate in size between I. extensum and /. excavatum from which 
it is distinguished by the quite different conformation of the molars and 
premolars, especially on the outer side. The premolars have the two 
antero-external crests a little broader but lower, without projecting beyond 
the plane of the outer face, separated by a shallow groove and followed 
by a groove identical with the preceding one, whence it results that the 
external side of these teeth has three low vertical elevations separated by 
two shallow grooves which produce a gently undulating appearance very 
different from that seen in I. extensum and /. excavatum . The true 
molars are even more different, since the two antero-external crests are 
completely fused into a single convex column which is quite broad. Each 
molar has thus externally two low columns corresponding to the two in- 
ternal lobes, separated by a shallow depression opposite to the deep fur- 
row of the inner side. The posterior upper molars, and especially M-, 
have much compressed crowns. The dental series is almost straight. 
Diameters of P- .0035 X .0025 ; P A .0037 X .003 ; M 1 .004 X .0027 ; M- 
.004 x .0024 ; M- .004 X -002 ; length of space occupied by the five last 
upper molars .0185 (’89, 473). 
Interatherium lamellosum (Ameghino). 
Icochilus lamellosus Amegh.; Enum. Synoptique, etc., p. 15, 1894 ; Se- 
gundo Censo, etc., p. 150, 1898. 
Species of small size. The superior canine is well developed, of the 
same size and almost of the same form as the external incisor. They are 
separated the one from the other by a small diastema. These two teeth 
are laterally compressed and have the form of trenchant blades. The 
external incisor, or third, is separated from the second by a considerable 
diastema. Another diastema, a little longer, separates the first premolar 
from the canine. P- is placed opposite P- and carries a vertical groove 
with its angle antero-external. Length from anterior border of I 1 to pos- 
terior border of M- .037 (’94, 15-16). 
Interatherium multident atum (Ameghino). 
Icochilus multidentatus Amegh.; Enum. Synoptique, etc., p. 17, 1894; 
Segundo Censo, etc., p. 15 1, 1898 (listed). 
Quite small. It is distinguished in having eight molars above and 
below on each side, of which the five anterior teeth are premolars. In 
