120 



UNGULATA 



ORDER VII 



little known. Basal Eocene ; Puerco and Torre j on beds, 



cusps. Skeleton 

 New Mexico. 



The largest species attained the size of the fox. 



The crescentic form 

 of the external cusps 

 of the lower molars 

 is very distinctive. 

 It is probable that 

 these forms mark 

 the rise of the 

 artiodactyls. 



Mioclaenus Cope 

 (Fig. 149). Dental 

 series continuous. 



Premolars relatively short. M. turgidus, acolytus Cope. M. lemuroicles Matthew. 

 Protoselene Matthew. Premolars compressed (P. opisthaca Cope). 

 Oxyacodon Osborn and Earle (Anisonchus agapetillus Cope). Very simple 



short premolars. Lower molars quinquetubercular. Lowermost Eocene; 



Puerco beds, New Mexico. 



p3 



Mioclaenus lemuroicles Matthew. Lower Eocene of Torrejon beds. New Mexico. 

 A, Mandible, and B, upper tootli-row, P3_ jif3. i/^. (After Matthew.) 



Family 2. Periptychidae Cope. 



Upper molars tritubercular. Upper and lower premolars rather large, usually 

 single cusped, sometimes with a low internal tubercle. Tibial articular surface of 

 the short broad astragalus rounded, medially concave. Navicular laterally in contact 

 with calcaneum and cuboid. Lowermost Eocene ; Puerco and Torrejon beds, 

 New Mexico. 



According to Matthew, these forms, at least in the structure of their 

 extremities, are allied to -^ 



the Pantolambdidae and 

 belong, therefore, to the 

 Amblypoda, but they differ 

 widely in having buno- 

 dont molars. 



Periptychus Cope (Fig. 

 150). Teeth highly 

 specialised, enamel very 

 strongly developed. 

 Upper molars almost 

 quadrate. Premolars 

 very large, grooved verti- 

 cally. This form nearly 

 equalled the sheep in 

 size. Torrejon beds ; 

 New Mexico. 



Ectoconus Cope. Of equally large size as the preceding form ; and with 

 multituberculate molars. Puerco beds ; New Mexico. 



Haploconus, Hemithlaeus, Anisonchus (Zetodon) Cope, and Conacodon Matthew, 

 are all of smaller size. Upper molars much broader than long, v/ithout a 

 second internal cone, but with anterior and posterior cingula. Lower third 

 molars with a short talonid. Puerco and Torrejon beds; New Mexico 



Fig. 150. 



Periptychus rhahdodon Cope. Lower Eocene of Torrejon beds, New 

 Mexico. A, Upper cheek teeth. B, Right ramus of lower jaw. Vs- 

 (After Cope.) 



