198 THE DESEADO FORMATION OF PATAGONIA 
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. There- 
fore, 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 over- 
lapping 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 SHIELD | MOVABLE PLATES | PELVIC BUCKLER | ORNAMENTATION 
Proeutatus Plates thin, coarsely|Plates thick, } over-|8 + probably 10) ‘‘Flask”’ figure 
pitted lapped rows 
Prozaedius Plates thin, finely|14 bands, thin, 4/8 rows \3 long ridges, 
pitted overlapped median ridge nar- 
row 
Stenotatus Plates thick,coarsely|Plates thick and/1r rows l3 long ridges, all 
pitted wide subequal 
Proeuphractus + overlapped No buckler 
Peltephilus 19 or 21 Plates 2 or 4;/Wide and thin 2-4)Buckler Large shallow pits 
horns wide pits 
Proeutatus Ameghino 
Eutatus Amegh., in part, 1887, Bol. Mus. La Plata, t. 1, p. 25. 
Proeutatus Amegh., 1891, Revista Argen. d. Hist. Nat., t. I, 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. 
This is the most frequently occurring genus in the 
Deseado, but is as yet represented only by isolated plates. 
