While rare, this genus is well known from the Santa Cruz, and is characterized by the curious development of the head shield, which consists of nineteen or twenty-one definitely arranged head plates, the anterior ones being developed into horn-like projections. The plates of the carapace are wide, thin, and unique in each having two to four wide shallow pits on the exposed surface. We found the genus rare, only two isolated plates turning up. From the Deseado material Ameghino has made three species: _P. protervus_, of very large size; _P. undulatus_, of moderate size, with the median figure accentuated and ending in two pits and with piliferous depressions on the margin; and _P. depressus_, of the same size as the foregoing, with a faint central figure, often four pits on the exposed surface and no piliferous pits on the margin. We found but one species, one plate of which combines characters of both the last two as described, so that I feel that there should be but two species, _P. protervus_ and _P. undulatus_. =Peltephilus undulatus= Ameghino [Illustration: Fig. 133. Two movable plates—natural size.] P. undulatus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 509. P. depressus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 510. One of the plates we found has the rough surface, obscure figure, two pits on the median part of the surface, and marginal piliferous pits, of which the first two features are characters of _P. undulatus_, the last is the feature of _P. depressus_, so I have combined the two species. A second plate does not have the marginal pits but is otherwise the same. I expect considerable variation in the pattern on plates from different regions of the carapace. =Peltephilus protervus= Ameghino P. protervus, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 509. This species, of which we found no representative, is very large. The plates of the type have two pits on the anterior part of the exposed surface and none on the margin. A movable plate measures 41 mm. long by 22 mm. wide. One of the horn-like plates from the cephalic shield is 35 mm. long, by 30 mm. wide, and has a height of 44 mm. GLYPTODONTIA This suborder is most sparingly represented, apparently on account of unfavorable habitat. Ameghino has described a few fragments of the carapaces of these forms, making the genera, _Palaeopeltis_, and _Glyptatelus_, both pre-Santa Cruz genera. =Palaeopeltis= Ameghino Palaeopeltis Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 659. The basis of this genus is a few plates of a glyptodon-like animal of considerable size, but the plates are without ornamentation. This form Ameghino considers intermediate between glyptodonts and armadilloes. I feel that there is too little of the skeleton known to justify this conclusion, especially as glyptodonts of a considerably higher grade of specialization are contemporaries of this form. [Illustration: Fig. 134. P. inornatus: a single plate—natural size.]