88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



tion with teeth so that their allocation is speculative and based on 

 relative abundance. These elements were figured and briefly de- 

 scribed by Teilhard de Chardin (1921-1922), and certain of them 

 were compared by Simpson (1929) to Meniscotherium. The distal 

 part of the humerus figured by Teilhard de Chardin resembles that of 

 Meniscotherium although the crests of the trochlea are less pro- 

 nounced and there is evidently no entepicondylar foramen as Simpson 

 noted. The proximal position of the lesser and third trochanter and 

 the shortness of the digital fossa of the femur are rather unlike Menis- 

 cotherium, and I note in this a greater similarity to the recent 

 hyracoids. The distal extremity of the femur is also rather dissimilar 

 in the relatively smaller condyles. The shorter and wider patellar 

 groove noted by Simpson is also suggestive of the hyracoids. The 

 long, slender, and nearly straight ilium with the little-developed 

 anterior inferior spine adjacent to the acetabulum is decidedly unlike 

 Meniscotherium. I note that the calcaneum has a rather prominent 

 peroneal tubercle and a large and rather elongate astragalar condyle, 

 but the anterior portion of the bone is relatively short, although the 

 astragalus has an elongate neck as in Meniscotherium. The sustentac- 

 ular facet extends far forward on the neck of the astragalus, and 

 the ectal facet is oval concave and nearly transverse, somewhat 

 more as in Tetraclaenodon in this latter respect. Simpson regarded 

 the presence of an astragalar foramen in Pleuraspidotherium as 

 distinctive. We now know, however, that this foramen is present 

 in the astragalus of Meniscotherium as well. 



Orthaspidotherhtm offers many more problems in its comparison 

 with Meniscotherium, and the character of the lower teeth is rather 

 inconsistent with any rather close relationship to Pleuraspidotherium. 

 Their artiodactyl-like structure is rather striking. A close relation- 

 ship to Pleuraspidotherium has been postulated on the close resem- 

 blance of the upper teeth. An interpretation of homologies of cusps 

 of the upper teeth suggested by Simpson would not be inconsistent 

 with a supposition of artiodactyl affinities for Orthaspidotherium. 

 Nevertheless, foot bones attributed to Orthaspidotherium by Teilhard 

 de Chardin, if correctly assigned, would scarcely be compatible with 

 an artiodactyl relationship. 



It has been suggested to me that possibly Protoselene is ancestral 

 to Meniscotherium. In a comparison of these two it would seem that 

 the teeth of Protoselene possess a distinct potentiality for such a 

 development. Nevertheless, the change required is rather striking in 

 degree for an interval such as between Torrejonian or early Tiffanian 



