Cope.) 398 [April 15, 
MACRAUCHENIID &. 
But one genus of this family is known at the present time. The follow- 
ing are the dental characters of Macrauchenia. Formula: I. $; C.+; 
P.m. ¢; M. 3, forming an uninterrupted series. The superior molars pre- 
sent two external Vs, and two oblique transverse crests, somewhat as in 
Palgotherium. The spinous foramina pierce the neural arch of the dorsal 
vertebre (Gervais). There is no intertrochlear crest of the humerus, but 
the carpal facets of the radius are well distinguished. The internal malleo- 
lus is small, but the fibular malleolus is codssified with the tibia at an early 
age, and articulates with the calcaneum. The trochlea of the astralagus 
is well developed. The Jateral digits are large, and the distal keels of the 
metapodials are continued on the anterior face of the condyle. 
The position indicated by the above characters is a remarkable one. The 
uninterrupted dental series and the absence of intertrochlear humeral 
crest, are primitive features among ungulate Mammalia, The radiocarpal 
articulation is facetted as in higher ungulates, but lacks the inferior condy- 
loid face of those types. The completeness of the metapodial distal keels 
is a feature of high specialization, only seen in the Hquid@ of this order. 
The codssification of the external malleolus is also a character peculiar to 
the Hguide among the Perissodactyla. There are two other characters 
which are not elsewhere found in this order, viz: the articulation of the 
fibula with the calcaneum, and the absence of the vertebrarterial canal. 
The former belongs to the Artiodactyla generally, and to the Proboscide, 
and the latter to the ruminant family of the Camelide. Thus the Macrau- 
chentide stand out as one of the most distinct of the families of the Perisso- 
dactyla, and one to which we may anticipate considerable accessions in 
future. 
But two species of Macrauchenia are known, a larger, M. patachonica, 
and asmaller, M. baliviensis, both from the Pliocene formation of South 
America. 
PALZOTHERIID A. 
This family has been already defined on page 378. In its complex pre- 
molar teeth, which in the upper jaw resemble the molars in composition, 
it shows an advance over the Chalicotheroid and other genera of the Lower 
Eocene. In fact, it has not been found in the Lower Eocene, but com- 
mences in the Upper Eocene in the genera Paleotherium and Paloplothe- 
rium. Thence it extends to the very summit of the Miocene, and may 
even occur in the European Pliocene (Protohippus). Its members exhibit 
considerable range of variation in the details of the teeth and feet, but no 
striking break of family importance occurs. The most noteworthy inter- 
ruption is that which is found between the Puleothering and Hippotheriina, 
where there isa change in the form of the proximal extremity of the 
humerus from a tapiroid to a horse-like form, and a modification of similar 
significance in the molar teeth, by the addition of a deposit of cementum. 
