SCOTT : ENTELONYCHIA OF THE SANTA CRUZ BEDS. 265 
with the occipital crest on the other. This lateral portion is inflated and, 
partially at least, filled with cancellous bone. The posterior portion, 
which makes up part of the occipital surface, is also much inflated and 
contains a sinus, which no doubt communicates with the cavity of the 
tympanic bulla, as in Nesodon , though I have not been able to make sure 
of this communication. This occipital exposure is relatively narrower 
and the occiput proper wider than in the Toxodonta, while in the Typo- 
theria the true occiput is much broader and the post-tympanic narrower 
than in either of the other suborders. 
The zygomatic process also differs in certain details from that of Neso- 
don , though, as in that genus, it has considerable resemblance to the 
same structure in the rhinoceroses, being rather thin and compressed, 
but very deep dorso-ventrally, giving it quite a massive appearance when 
seen from the side. It does not have the steep anterior descent seen in 
the Santa Cruz Toxodonta, but the dorsal border rises moderately for- 
ward to a point about the middle of its course and thence, in one of the 
skulls, descends anteriorly, while in the other it rises gently almost to 
the boundary of the orbit. In Adinotherium and Nesodon the process 
ends abruptly in front and is received into a shallow notch of the jugal, 
forming little or none of the orbital boundary, while in Homalodonto- 
therium it is relatively longer, does not notch the jugal, but rests upon it 
and narrows anteriorly to a blunt point, forming the posterior and much of 
the inferior boundary of the orbit. The dorsal border descends very 
abruptly in a concave curve to make the posterior orbital boundary. 
The jugal is a large and heavy bone, with great dorso-ventral depth 
and with its ventral border projecting downward freely, so as to conceal, 
in side view, the alveolus of m- and, in the young skull, of m- as well. 
In the Toxodonta there is no such prominent projection of the ventral 
border. As already mentioned, the jugal is not excavated to receive the 
anterior end of the zygomatic process, but extends beneath that process 
almost to the glenoid cavity, where it terminates in a rounded end. The 
jugal forms some of the inferior and nearly the whole anterior margin of 
the orbit. 
Though agreeing in essentials with that of Nesodon , the tympanic has 
a very different appearance, whether viewed from the side or from below. 
The inflated bulla is much larger than in that genus, especially in antero- 
posterior diameter and, in ventral view, forms an elongate, narrow oval. 
