SINCLAIR : TYPOTHERIA OF THE SANTA CRUZ BEDS. 
105 
is very short. I x is very large and I- and I- very small. The canine is 
well developed. Length from the anterior part of I 1 to the posterior part 
of M- .027 (’94, p. 18). 
Interatherium rodens (Moreno) Ameghino. 
Interatherium rodens Moreno ; Patagonia, resto de un antiguo continente 
hoy submerjido, p. 23, 1882 [nomen nudum). Ameghino; Observa- 
ciones generales sobre el orden de mamiferos estinguidos sud-ameri- 
canos llamados Toxodontes, etc., p. 63, 1887; Enumeracion Sis- 
tematica, etc., p. 15, 1887; Contrib. al Conoc., etc., pp. 467-468, 
PI. 15, figs. 20-26, 1889; Enum. Synoptique, etc., p. 18, 1894 
(listed); Segundo Censo, etc., p. 151, 1898 (listed). 
Size of a. rabbit. Represented by numerous fragments of mandibles 
and the anterior part of a skull with almost all the dentition. The pre- 
maxilla is short and thick. I x is three millimeters wide at the base of the 
crown. The base of I- is two millimeters and that of I- less than one 
millimeter. The base of the crown of the canine is also less than one 
millimeter. P 1 is very small, almost rudimentary and of an acutely con- 
ical shape ; it is closely appressed to P-. P- has a more elongate crown. 
It has a small internal groove which dies away on the base of the crown 
before reaching the root, dividing the crown into two internal lobes, the 
anterior much smaller than the posterior. On the anterior part of the 
outer side is a deep and narrow groove which hardly extends to the base 
and divides the crown into two external lobes, the anterior very narrow 
and ridge-like, the posterior much broader. P- and P-, successively 
larger, have the same general form but with the inner lobes more equal. 
The three premolars with very long crowns have the bases divided into 
separate but very short roots. The true molars have an internal groove 
like the premolars, which extends to the base, dividing the crown into two 
equal lobes. The antero-external groove also extends to the base, but 
near the middle of the anterior face there is a second broader groove 
forming three well-marked external columns. The three true molars are 
completely open at the base. The seven molars form a much more pro- 
nounced arc of a circle than in the following species. The symphysial 
part of the mandible, much compressed laterally, has the incisors and 
canine in continuous series and inclined forward. Only I T is placed in 
the anterior narrowest part of the symphysis, with its crown transverse. 
