520 GEOLOGICAL SURVEY OF THE TERRITORIES. 



ToMAECTUS BREvmosTEis, Cope, Pal. Bull., No. 16, p. 2. 



Second premolar two-rooted. Anterior half of the carnassial with the 

 usual sectorial structure ; the anterior lobe the smaller. The inner 

 tubercle bout the same height. The heel constitutes one-third the 

 length of the tooth, and its lateral tubercles are angular; the posterior 

 low. Enamel slightly rugose. 



Measurements. 



M. 



Length of first three molars 0.041 



Length of thiitl molar, (carnassial) 033 



Elevation of third molar, (carnassial) 014 



Width of third molar at middle 009 



Length of heel of third molar 007 



Depth of ramus at third molar 021 



In the abbreviation of the dental series in front, this species resem 



MARTES, Cuv. 



Martes mustelinus, Cope, Pal. Bull.,* No. 14. {^lurodon.) 



A small, single-rooted, second molar of the lower jaw. First molar 

 sectorial, with a rather narrow posterior heel, one-third its length, and 

 a small inner tubercle at the base of the second outer cusp. Last pre- 

 molar with a short posterior heel, and distinct outer tubercle on the 

 posterior side of the cusp. Margin of jaw strongly everted below mas- 

 seteric fossa. 



Measurements. 



Length of three last molars 0.018 



Length of sectorial molars 010 



Width of sectorial molars, (greatest) 005 



Height of posterior cusp, (greatest) 005 



This species was about as large as the domestic cat, and less than 

 one- third that of JElurodon ferox, Leidy. 



PERISSODAOTYLA. 



AOERATHERIUM, Kaup. 



AcERATHERiUM MEGALODUS, Cope, Pal. Bull., No. 14, p. 1. 



This large species and the A. crassus, Leidy, were very abundant dur- 

 ing the Pliocene period in Western North America. Their remains are 

 everywhere mingled with those of horses and camels. The former, and 

 probably the latter, are to be referred to a distinct section of Acera- 

 iherium on account of the existence of but three premolar teeth in the 

 mandibular series, and probably in the maxillary also. One of our speci- 

 mens exhibits the missing superior premolar on one side. The outer 

 incisor below is a large tusk, while the inner is small and caducous, 

 points in which this genus resembles the genera above named, and dif- 

 fers from the African and tichorhine species, or genus Atelodus of 

 Pomel. 



A posterior upper molar represents the A. crassus in the original col- 

 lections described by Leidy. A w^ell- developed tubercle, which rises 



* These publications may be procured at the Naturalist's agency, Salem, Mass., or of 

 the writer. 



