Of the hind limb, Gaudry[16] figures the astragulus and the calcaneum, the former short and with a low trochlea, the latter also short and with a broad facet for the fibula. Gaudry also states that the foot was tridactyl and plantigrade, but I am doubtful of the plantigrade feature. [Footnote 16: Annales Palaeontologie, 1906, t. 1, p. 28.] Ameghino has made six species of this genus, _L. gaudryi_, _L. fissicola_, _L. lapidosa_, _L. oxyrhynca_, _L. stenognatha_, and _L. garzoni_. All of the first five are described as of the same size as _L. gaudryi_. _L. garzoni_ is a smaller, about 60 per cent. of the size of the others. Of the first five listed, the first three have the large incisor and I consider them all _L. gaudryi_. _L. oxyrhynca_ and _L. stenognatha_ are described as having small canines and I believe that this is a sexual difference only, so have considered these two species as also belonging to _L. gaudryi_, but females. I have made a careful comparison of _L. gaudryi_ and _L. oxyrhynca_ and find them identical in all the features except in the region of the canines where the latter is weaker, and can see no more than sexual differences. Usually with this weakness of the canine goes a smaller or lighter build of the lower jaw which is what would be expected. The points by which the various species were differentiated were, beside the size of the canine, the presence or absence of pit 3, and the variation in the foldings on the outer sides of the lower molars, which I find on sectioning a tooth appear deeper or shallower according to whether the tooth was more or less worn. =Leontinia gaudryi= Ameghino L. gaudryi Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 648. L. gaudryi Amegh., 1897, Bol. Geog. Argen., t. 18, p. 472. Scaphops grypus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 629. Scaphops grypus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 475. Steniogenium sclerops Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 654. Steniogenium sclerops Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 475. Leontinia fissicola Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 474. L. (Senodon) lapidosa Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 649. Females L. oxyrhynca Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 472. L. stenognatha Amegh., 1897, Bol. Inst. Geog. Argen., t. 15, p. 474. Colpodon gaudryi Gaudry, 1906, Anal. Palaeontologie, t. 1, p. 30. [Illustration: Fig. 69. Right upper dentition—½ natural size.] [Illustration: Fig. 70. Lower dentition of male—½ natural size.] [Illustration: Fig. 71. Lower dentition of female—½ natural size.]