Cope.J ^^O [April 15, 



MACRAUCHENIID^. 



But one genus of this family is known at tlie present time. The follow- 

 ing are the dental characters of MacraucTienia. Formula : I. f ; C. -^ ; 

 P.m. I ; M. f, forming an uninterrupted series. The superior molars pre- 

 sent two external Vs, and two oblique transverse crests, somewhat as in 

 Palceotherium. The spinous foramina pierce the neural arch of the dorsal 

 vertebrae (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 coossified with the tibia at an early 

 age, and articulates with the calcaneum. The trochlea of the astralagus 

 is well developed. The lateral 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 Equidce of this order. 

 The coossification of the external malleolus is also a character peculiar to 

 the Equidce 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 Proboscidse, 

 and the latter to the ruminant family of the Camelidm. Thus the Macrau- 

 cheniidoB stand out as one of the most distinct of the families of the Perisso- 

 dactyla, and one to which we may anticipate considei'able accessions in 

 future. 



But two species of Macrauchenia are known, a larger, M. patacJionica, 

 and a smaller, M. haliviensis, both from the Pliocene formation of South 

 America. 



PAL^OTHERIID^. 



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 Chalkotheroid 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 PalcBotJierium and Paloplothe- 

 rium. Thence it extends to the very summit of the Miocene, and may 

 even occur in the European Pliocene (ProtoJiippus). 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 Palceotherince and HippotJieriincB, 

 where there is a 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. 



