Ancylocoelus Ameghino

This genus differs from Leontinia in its formula,

but, except for the loss of these canines and the lower premolars, is very similar. In this it seems to approach the line which gave rise to Colopdon. The premolars and molars are also narrower in proportion than in Leontinia. I have placed Rodiotherium also under this genus as I can not see a generic difference in the descriptions. However we were not fortunate enough to find these forms. Ameghino has described four species as follows:

A. frequens, 1895, Bol. Inst. Geog. Argen., t. 15, p. 475.
Upper dentition, pm. 1 to m. 3150 mm.
Lower dentition, pm. 2 to m. 3150 mm.
Upper molar 3, length39 mm.
A. lentus, 1901, Bol. Acad. Nac. Cordoba, t. 16, p. 407.
Upper molar 3, length48 mm.
A. minor, 1901, loc. cit.
Upper molar 334 mm.
A. (Rodiotherium) armatum, see cit. above.

Based on an imperfect mandibular symphysis, in which incisor 3 is very large.

CHAPTER VIII
Nesodontidae

This family is characterized by the teeth being hypsodont, the second upper incisor and the third lower incisor being enlarged into caniniform teeth, the upper molars complicated by the development of cristae, limbs short, feet tridactyl and semidigitigrade.

Fig. 79. A, upper and a lower molars 2 of Proadinotherium;
B, upper and b lower molars 2 of Coresodon;
C upper and c lower molars 2 of Neudon—
½ natural size.

In the Santa Cruz, the family is represented by the two genera Nesodon and Adinotherium. In the Deseado we find Proadinotherium evidently ancestral to Adinotherium and very little differentiated from it. Ameghino has described a genus, Pronesodon, which is evidently ancestral to Nesodon. I have referred Coresodon to this family because the molars of the upper and lower jaws are very close to those of Adinotherium. Ameghino has also described two genera, Nesohippus and Interhippus, based on upper molars which are very similar in pattern to Adinotherium and which I believe belong to this family, if they prove to be valid genera, of which I have some doubt, feeling that they will prove to be the deciduous upper premolars of Proadinotherium or some similar form. The genus Senodon, which Ameghino also places in this family, I feel will prove to be worn teeth of Leontinia.