75 

 Measurements taken from the lower-jaw specimen are as follows : 



Inches. Lines. 



Distance from incisive alveoli to back of last molar 4 10 



Space occupied by tbe molar teeth, estimated 4 



Space occupied by the true molars 2 7 



Fore and aft diameter of last molar ■ 1 1 



Depth of jaw at second molar 1 6 



Thickness of jaw below second molar 10 



Estimated length of lateral incisors 3 3 



Depth of symphysis following its slope 2 10 



Tkogosus vetulus. 



An apparent smaller species of Trogosus is indicated by the fragment of an 

 incisor tooth, represented in Fig. 43, Plate VI. The specimen was discov- 

 ered by Dr. Carter in the vicinity of Fort Bridger, and sent to the writer last 

 summer. _ It consists of the exserted portion- of the tooth, and agrees in form 

 and proportions with the corresponding portion of the incisors in the jaw- 

 specimen above described. The enamel is smoother, but invests the tooth to 

 the same relative extent. The antero-posterior diameter of the tooth has 

 been about 8 lines ; the transverse diameter 4 lines. 



HYOPSODUS. 



Hyopsodds paulus. 



One of the smallest of pachyderms, referred to a genus and species above 

 named, is established on many specimens, chiefly consisting of portions of 

 lower jaws with teeth, (Figs. 1 to 9, Plate VI.) It was originally indicated, 

 from a lower-jaw fragment with teeth (Figs. 1, 2) of an old animal, discov- 

 ered by Professor Hayden, in 1870, in the vicinity of Fort Bridger, Wyo- 

 ming. Since then the writer has received a number of more characteristic 

 specimens, obtained by Dr. J. Van A. Carter and Dr. Joseph K. Corson, at 

 Grizzly Buttes, Henry's Fork of Green River, Lodge-Pole Trail, and other 

 localities in the neighborhood of Fort Bridger, Wyoming. 



The animal was rather less in size than the Aphelotherium Duvernoyi of 

 Gervais, the remains of which were found in the gypsum quarries of Paris, 

 France. It also appears to have been allied to this, as indicated by the num- 

 ber, relation, and constitution of the teeth. Both Aphelotherium and Hyop- 

 sodus possessed unbroken arches of teeth to the jaws, as in the Anoplothe- 

 rium, whose remains are found in association with those of the first-named 

 genus. 



