416 THE PUERCO EPOCH. 



Buperior molar series of two of thein is known. The distinctive characters 

 of the former are as follows: 



I. No anterior median tubercle of inferior true molars. 

 a. Fourth inferior premolar robust. 



Leujith of last four molars M. 018; of true niolais ii and iii, .0082 H. angitstus. 



LiiU'^lh of last four molars, .OJl'; of true molars ii and iii, .010; third and fourth pre- 

 molars equal E. lineatus. 



aa. Fourth inferior jireinolar compressed and sharp. 

 Length of last four molars, .020; third premolar shorter than fourth H. xiphudon. 



II. Anterior median tubercle present. 



Anterior median cusp smaller; last four molars, .024; true molars ii and iii, .0115; 

 largest H. entocomis. 



The characteristics of tlie superior molars of two of the species are as 

 follows : 



I. Internal lobe of fourth superior premolar crest-like and concentric. 



True molars less transverse; length .012; ])remolars striate H. lineatus. 



II. Internal lobes of fourth i)remolar conic. 



Time molars more transverse; length, . 0145; premolars smooth H. entoconus. 



All the species are from the Puerco Eocene. 



Haploconus angustus Cope. 



Mioolcenut angiutua Cope. American Naturalist, 1881, 831, Sept. 22. Paleontological Bulletin No. 33, 



p. 491. 

 Plate LVII/; fig. 6. 



The least species of the genus, with the teeth about the size of Hyopso- 

 dus pauhts Leidy, but with more robust jaw. The molar teeth diminish in size 

 regularly posteriorly from the P-m. iv. They all have three subequal pos- 

 terior cusps which are less elevated than the anterior ones. The median is 

 enlarged into a heel on the last tooth. The anterior are opposite, and the 

 external is larger than the internal. There is no anterior internal. The 

 external wears into an anteroposterior narrow grinding surface, which looks 

 like a combination with an anterior median. The latter is, however, not 

 separate on the least worn molars. The anterior outer cusp increases in 

 size anteriorly, and is the large cusp of the P-m. iv. It sends a branch 

 backwards on the inner side of the crown which forms the edge of the nar- 

 row concave heel. There are no cingula except a short one on the anterior 

 corners of the base of the crown of the P-m. iv. Enamel obscurely 

 wrinkled. 



