Sinclair: typotheria of the santa cruz beds. 
103 
the upper jaw, the canine and the first two premolars are very small and 
in continuous series with the other teeth. In the lower jaw, the first two 
premolars have the form of small canines and the second is separated 
from the third by a small diastema. The first two lower premolars and 
the canine are unspaced. Length of space occupied by the eight upper 
molars .028 (’94, 17). 
Interatherium interruptum Ameghino. 
Interatherium interruptum Amegh. ; Enurn. Synoptique, etc., p. 18, 1894 ; 
Segundo Censo, etc., p. 15 1, 1898 (listed). 
Size of I. supermini. Distinguished easily by the presence of the first 
upper premolar which is placed against the anterior part of P-, and by the 
complete absence of the canine. There is a long diastema which sepa- 
rates the first premolar from the external incisor. The margin of this 
diastema carries a deep longitudinal groove which has the same direction 
as the dental series. Length of the seven upper molars .025 (’94, 18). 
Interatherium curtum (Ameghino). 
Icochilus curtus Amegh. ; Enum. Synoptique, etc., p. 17, 1894; Segundo 
Censo, etc., p. 15 1, 1898 (listed). 
Of the same size as I. extensum. This species is easily distinguished 
by the great shortening of the last lower molar which is hardly longer 
than and by its posterior lobe which is convex on the external side 
without vestige of the perpendicular groove seen on the same tooth in the 
other species. is nearly .005 long. The last two molars occupy a 
space of .009 (’94, 17). 
Interatherium crassirame (Ameghino). 
Icochilus crassiramis Amegh. ; Enum. Synoptique, etc., pp. 16-17, 1894 ; 
Segundo Censo, etc., p. 15 1, 1898 (listed). 
Of the same size as /. extensus. Distinguished very well by the first 
lower premolar which has the form of a well-developed canine, being iso- 
lated in front and behind by fairly large diastemata. The lower canine 
has the form of an incisor, resting anteriorly on the external incisor. The 
second lower premolar is elliptical, without perpendicular internal groove. 
Of the outer groove only traces are visible (’94, 16-17). 
