J. B. Hatcher — Recent and Fossil Tapirs. 171 



tionately narrower than in those referred to C. dakotensis. 

 The present specimen is from the Oreodon beds, below the 

 Metamynodon layer. 



Milk dentition : Portions of two lower jaws (Nos. 10507 

 and 10506, fig. 2 and 7, plate III) in our collection are of 

 interest, inasmuch as they show successive stages in the erup- 

 tion of the milk and permanent dentitions. In 10507 the first 

 milk molar has been broken off and lost, but the second and 

 third are still in place, and immediately behind them is the first 

 permanent molar fully erupted and behind it m. 2 may be 

 seen just commencing to cut the gum. Beneath the decidu- 

 ous molars and the anterior half of the first permanent molar, 

 the bone from the inside of the jaw has been removed, expos- 

 ing the unborn premolars in position. By a glance at fig. 2, 

 plate III, it will at once be seen that these teeth, as well as per- 

 manent molar 2, occupy a position in the ramus considerably 

 posterior to that which they will assume w T hen fully erupted. 

 In other words, in the process of eruption they will move for- 

 ward and upward. No. 10506 has all the deciduous molars in 

 place and the first permanent molar just coming into place. 

 As has been remarked by O. & W., the last two milk molars 

 closely resemble the permanent set, while the first is like the 

 corresponding premolar. These specimens were found by Mr. 

 J. W. Gridley in the upper Titanotherium beds. 



Measurements of C. occidentalis (JVo. 10953 Princ. Coll.) 



Length of inf. premolar-molar series 82 mm 



" " " series 32 



" " molar " 50 



" last inferior molar ._ _ 21 



Colodon dakotensis, O. & W. 



In describing this species, Osborn and Wortman have 

 described the postero-internal cusp of the last lower premolar 

 as double, placing considerable importance upon this character, 

 and the absence of external and internal basal cingula on the 

 superior premolars. The double character of the postero-internal 

 cusp of the last lower premolar is, probably, of little importance, 

 since in their collateral type specimen it is very faint, and has 

 more the nature of a basal cingulum than of a cusp, and more- 

 over, a similar state of affairs is noticeable on some of the 

 smallest of our specimens, referred to C. occidentalis. Too 

 much importance should not be given to the presence or 

 absence of basal cingula, which have been shown by Nathusius* 

 to depend, in living animals, largely npon the abundance or 



* See Der Schweinschadel. 



