42 

 Measurements. 



B. priscidens. B. planiceps** B. nehraicensis** 



MM. MM. MM. 



Upper molar series, length 62 103 TO 



Upper premolar series, length . 62 



Ml width, (tr.) 23-2 35 26 



M2 « 24-5 36 28 



M3 " 24 37 26 



Ml length (ap.) 22 



M2 " 23 3) 27 



M3 » J9-5 40 



Piwidth(tr) - 13-5 



P2 " 20 



P3 " , 21-7 



pi " 23 



pi length (a.p.) 12-3 



P2 " 16 



ps » 16-8 



pi " 17-3 



The anterior end of the mandible of a Hyracodon, obtained in 1904 from the Bone Coulee 

 beds, is of special interest ; it is provisionally assigned to this species. 



The specimen (plate IV, figures 3 and 4) consists of nearly half the left ramus with that 

 part of the right ramus anterior to the second premolar. Premolars 2, 3 and 4 are preserved, 

 as well as the roots of the canines, and of the three pairs of incisors. The alveolus ot the 

 second premolar is partly seen on the right side. 



A striking feature is the long diastema, between the canine and the second premolar, 

 nearly equal to that of Hyrachyus (H. agrarius) in proportionate as well as actual length, and 

 about twice as long as that oi Hyracodon nebrascensis,'Le\dy. A basal cingulum is continuous 

 round the entire crown of the premolars, except for a short distance internally, in the second 

 and fourth teeth, posterior to their mid-length. 



Measurements. 



MM. 



Length of premolar series 44 



Premolar 2: — 



Antero-posterior diameter * 13 



Transverse diameter , 10 



Premolar 3: — 



Antero-posterior diameter , , 15 



Transverse diameter , . . . . 12 



Premolar 4: — 



Antero-posterior diameter. . .• 1 6 • 5 



Transverse diameter , 13-5 



Depth of ramus in front of premolar 3 28 • 5 



Maximum thickness of ramus beneath same tooth 15 



Length of diastema behind canine 26 



Breadth of mandible at mid-length of diastema 21 



Length of symphysis g2 



Thickness of mandible near posterior end of symphysis 14 



* ♦The measurementB of the teeth of B planiceps and B. nebrasoen.m are taken from the " Preliminary account of the 

 FossilMamnjalsfrom the White River formation oontamed in the Museum of Comparative Zoology" by W. B., Scott an^ 

 Henry F. Osborn, 1887, p. m, Bull. IVfus. Comp. Zool., Harvard Colle|>e. ^ BO' J- " ■ x>., ^^u ^ ^ 



