The representatives of this group are so poorly known in the Deseado beds that Ameghino has, in general, used the generic names of the Santa Cruz for their description, and, so far as known, they are little differentiated from those genera. There is as yet no material which shows the association of skeletal parts with the carapaces. Therefore, in this paper, comparisons are made wholly on the carapace, with the expectation that the skeleton, when found, will correspond. The Deseado species are but little less specialized than the Santa Cruz, the carapace consisting of movable overlapping bands of plates both in the anterior and body portions, while over the pelvic region the plates are fixed, do not overlap, and form a pelvic buckler. Ameghino has described a considerable number of genera based on isolated plates, to which I refer later. The chief genera which occur in these beds are also found in the Santa Cruz, and the distinguishing features are as follows: =================================================================== | Cephalic | Movable | Pelvic | Ornament- | Shield | Plates | Buckler | ation -------------+-------------+-------------+----------+-------------- Proeutatus |Plates thin, |Plates thick,| 8 + |“Flask” | coarsely |⅓ overlapped |probably | figure | pitted | | 10 rows | -------------+-------------+-------------+----------+-------------- Prozaedius |Plates thin, |14 bands, |8 rows |3 long ridges, | finely | thin, | | median ridge | pitted |¼ overlapped | | narrow -------------+-------------+-------------+----------+-------------- Stenotatus |Plates thick,|Plates |11 rows |3 long | coarsely | thick | | ridges, | pitted | and wide | | all | | | | subequal -------------+-------------+-------------+----------+-------------- Proeuphractus| |¼ overlapped |No buckler| -------------+-------------+-------------+----------+-------------- Peltephilus |19 or 21 |Wide and thin|Buckler |Large | Plates | 2-4 wide | | shallow | 2 or 4 | | | pits | horns | | | -------------+-------------+-------------+----------+-------------- =Proeutatus= Ameghino Eutatus Amegh., in part, 1887, Bol. Mus. La Plata, t. 1, p. 25. Proeutatus Amegh., 1891, Revista Argen. d. Hist. Nat., t. 1, p. 327. Thoracotherium Mercetat, 1891, Revista Mus. La Plata, t. 2, p. 42. Eutatus Lydekker, in part, 1894, Anal. Mus. La Plata, t. 3, p. 62. Proeutatus Scott, 1903-5, Reports Princeton Patagonian Exp., vol. 5, p. 40.