scott: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
259 
sideration and the Santa Cruz forms, such as Nesodon and Adinotherium , 
employed, since in them the essential characteristics of the toxodont den- 
tition are much more clearly displayed. From the dentition of the Santa 
Cruz toxodonts that of Homalodontotherium differs: (1) in the relatively 
unmodified form of the incisors and canines; (2) in the brachyodont 
character of the dentition ; (3) in the presence of the cingulum on all of 
the teeth, though very incomplete in some cases ; (4) in the much greater 
transverse width and consequently less compressed form of the grinding 
teeth; (5) in the somewhat less complex pattern of these teeth, due espe- 
cially, in the upper molars, to the shortening of the posterior crest and to 
the less prominence and early disappearance of the spurs (“combing 
plates”) from the external wall of the crown. In Nesodon the principal 
spur is very prominent and even in well-worn teeth divides the valley 
into two parts and give it its characteristic Y-like shape (see Pis. XV, 
XVII). 
The skull (Pis. XXVIII, figs. 1, 1 a\ XXIX, fig. 2) is quite small in 
proportion to the size of the trunk and the length of the limbs. The 
two specimens which I have had an opportunity to study have both suf- 
fered from distortion by pressure, though in different directions. That 
belonging to the type of H. segovice in the Ameghino collection which is 
shown in Plates XXVIII and XXIX, is very complete, but has been 
depressed and flattened by vertical pressure, making it appear to be 
unduly flat and low in the dorso-ventral dimension, as is clearly indi- 
cated by the shape of the orbit. A very young and imperfect skull in 
the Princeton collection (No. 16,014) lacking the preorbital portion, has 
undergone a lateral compression, which has diminished the transverse 
width and increased the dorso-ventral diameter. On this account the 
two skulls, at first sight, seem to have very different appearance and pro- 
portions. The skull of Homalodontotherium is essentially toxodont in 
character, differing only in a number of relatively unimportant details ; 
the very unusual and peculiar structure of the auditory region, which is 
common to all of the Toxodontia, is repeated in this genus, though in 
somewhat less pronounced fashion. 
The upper profile of the skull is nearly straight and horizontal through- 
out its length, but there may be present a slight descent at the forehead. 
The orbits have a forward position, with the anterior rim over m~, and 
the preorbital portion of the face is somewhat shorter than in Nesodon , 
