398 Bulletin American Museum, of Natural History. [Vol. XXVII, 



resemblances to the Horse, to Aceratherium and to Titanoiherium} Among 

 the chief Perissodactyl resemblances cited by Peterson are the following: 

 The general similarity of both deciduous and permanent cheek teeth to those 

 of Titanoiherium; the curiously horse-like character of the condylar foramen 

 and paroccipital process and of many features in the neck vertebrae: the 

 Perissodactyl facies of the sacrum; the resemblance of the scapula and pelvis 

 to that of Aceratherium; the possession of four digits in the manus and three 

 in the pes, the third digit being the longest in both, all as in Eocene Perisso- 

 dactyls; the general resemblance of the humerus, radius and ulna, femur 

 and pes to those of TitanotJterium. To this evidence may be added the 

 following considerations : 



(1) The dentition of Schizotherium Gervais," a European Oligocene 

 Chalicothere, shows evidence of derivation from an Eocene Perissodactyl 

 type. The premolars must have passed through a stage illustrated in 

 Lambdotherium. The molars have been evolved from a buno-lopho-seleno- 

 dont form not unlike that of the Palfeotheres. They must have attained 

 their definitive form through combined lengthening and compression, the 

 inner and outer cusps being brought nearer, even more than in the Upper 

 Eocene Titanothere genus Dolochorhinus, this causing the connecting cross 

 crests to be very oblique. 



(2) A very suggestive Perissodactyl feature is the funnel shaped fossa 

 running backward and inward from a point just internal to the postglenoid 

 process to the petrosal region. This curious fossa is very characteristic of 

 the horses and Titanotheres and is thought by Dr. C. S. Mead to have lodged 

 the internal extension of the meniscal cartilage. 



(.3) The foramen ovale is large and situated near the internal confines 

 of the glenoid surface, as in Titanotheres. 



(i) The carpus which is of the "displaced" type, retains as many 

 primitive features as could be expected in view of the great difference in 

 function between this heavily clawed digging manus and the normal Peris- 

 sodactyl type. It might be derived either from the Perissodactyl type 

 represented in Paloeosyops or from the Artiodactyl type represented in 

 Ancoclus but the height of the carpals favors the former view. In correlation 

 with the hypertrophy of the internal digit (II), the trapezium is unusually 

 laro-e but its scaphoid surface is still convex as in Perissodactyls and Artio- 

 dactyls. The internal process of the scaphoid (representing the centrale) 

 is verv broad, as in many Perissodactyls, the lunar has a nearly vertical 

 magnum facet and an oblique unciform facet as in both Perissodactyls and 



1 The valuable figures of the skull and skeleton of Moropus given by Barbour (1908) point 

 to the same conclusion. 



- Represented in the American Museum by casts showing the upper and lower cheek teeth 



