448 Marsh — A New Order of Extinct Mammals. 



The feet are primitive in type, and were apparently digiti- 

 grade, yet the terminal phalanges were not encased in hoofs or 

 in claws, but possessed an intermediate character, which has 

 suggested the ordinal name. Their extremities are thin, 

 somewhat expanded, and more like those of Primates than of 

 any other group. They were apparently covered by thin nails. 



The femur has a third trochanter, near the middle of the 

 shaft. The tibia resembles that of a carnivore. The fibula is 

 complete, well developed, and at its distal end is expanded, and 

 meets both the astragalus and the calcaneum. 



The hind foot is represented in figure 2, and presents several 

 points of interest. The astragalus and calcaneum are very 

 similar to those in Rodents. The navicular is supported entirely 

 by the astragalus, and the cuboid by the calcaneum. On the 

 tibial side below the navicular, and supported by it, is a small 

 bone (x) having beneath it the entocuneiform. It meets the 

 middle cuneiform also. This bone has apparently not been 

 known hitherto, and may be called the epicuneiform. It may, 

 perhaps, correspond to what is known as the tibial sesamoid in 

 Rodents and Carnivores, but its position and connection in the 

 present tarsus are quite different. Moreover, a distinct tibial 

 sesamoid is also present inside and behind the epicuneiform, 

 and hence not shown in the figure. 



In the feet of Meniscotherium, there are five well-developed 

 digits in manus and pes. The structure of the carpus and 

 tarsus agrees in general with that of Hyracops, but in some 

 points, there appear to be differences of importance. 



The order Mesodactyla contains at present the two genera 

 Meniscotherium and Ifyracops, which include primitive mam- 

 mals of small size, having the full number of forty-four teeth 

 in continuous series, with the premolars and molars similar in 

 type to mammals known as Ungulates. The limbs and feet 

 are primitive in type, unlike those of any known Ungulates, 

 and resemble those of Carnivores, or the early Primates. 



This order stands in somewhat the same relation to the 

 typical Ungulates that the Tillodontia do to Rodents, and the 

 Chalicotheria* to Edentates. Yery briefly defined,- the Meso- 

 dactyla may be considered as having the ungulate type of 

 dentition, with the limbs and feet of early Primates ; the 

 Chalicotheria as combining an ungulate dentition with the 

 feet of Edentates ; while the Tillodontia unite with the rodent 

 dentition the extremities of primitive Carnivores. These three 

 orders are quite distinct from each other and from the remain- 



* The name first proposed for this order, Chalicotheroidea, Gill, 1872, may 

 appropriately be shortened to Chalicotheria. The term Ancylopoda more recently 

 given is preoccupied. The genus Moropus is not identical with Chalicotherium 

 as has been vstated, and Morotherium, which has also been referred to the latter 

 genus, is a true Edentate allied to ilylodon. 



