530 GEOLOGICAL SURVEY OF THE TERRITORIES. 



M. 



Width of foitrth premolar, (half worn) ., 0.005 



Length of first molar, (half worn) -019 



Width of first molar, (half worn) .014 



Length of third molar -047 



Width of third anterior column .013 



In the second specimen the molars are a little narrower. 



Peoca]melus heterodontlts, Cope, Bull. U. S. Geol. Snrv. Terrs., 



1874, No. 1, 20. 



Eepresented by the right distal portion of a mandibular ramus, with 

 incisor, canine, and premolar teeth, and by the greater part of the den- 

 tition of the premaxillary and maxillary bones. These indicate an ani- 

 mal of the size of the species last described. 



An interesting fact in the structure of the genus is indicated by these 

 specimens, namely, that the premaxillary bones support a full series of 

 incisor-teeth, a fact not heretofore known, as the pieces in question had 

 not been previously identified by authors. The median incisors were 

 inserted into rather small sockets, and were separated by diastemata 

 from the third or caniniform incisor, from each other, and from the an- 

 terior extremity of the bone. 



A second result of the investigation is that the genus Homocamelus, 

 Leidy, is probably the same as Procamelus ; and that H. caninus should 

 "be regarded as the P. rohustus^ unless new evidence exists to the con- 

 trary. The former was established on dentition of the upper series 

 alone; the latter on that of the lower jaw. ■ In the present species, we 

 have the two kinds of teeth combined. The relations are, however, 

 quite different from tho^e found in the P. rohustus and the P. angusti- 

 dens. As to the reference of H. caninus to the former rather than the 

 latter of these two, it depends on their coincidence in the transverse 

 width of the premolar teeth, and is rendered probable by the fact that 

 they are from the same horizon and approximate locality. 



In the superior and inferior dentition of P. i^eterodontus, it is to be 

 noticed that the first premolar is situated well anteriorly, the space sep- 

 arating it from the second premolar being twice as long as that between 

 it and the canine ; in P. robustus, these interspaces are equal (in the 

 lower jaw) as in P. angustidens. In the present camel, the third incisor 

 is separated from the canine in the lower jaw by a space nearly equal 

 to that between the canine and first premolar ; in P. angustidens, and, 

 probably P. robustus, (= S. caninus,) this space is very much less, and 

 just sufficient to admit the superior caniniform incisor. In the present 

 species the lower border of the symphysis is below the canine^ and hence 

 the symphysis is much shorter than in P. angustidens, as it is steeper 

 and concave on the anteroinferior face. It is not co-ossified in the 

 specimen, while it is so in the P. angustidens. On each side of the suture 

 below is a small, compressed, descending tuberosity. The mental fora- 

 men is below the first premolar. The second and third lower premolars 

 are two-rooted and compressed ; the third presents an angle inward at 

 its anterior end. 



The premaxillary bones attenuated and simple in front, with little 

 indication of contact or connection across the middle line. The side of 

 the muzzle is concave above the first premolar. Last incisor vertical in 

 direction. 



The maxillary teeth associated with the above-described premaxillary 

 bones represent the entire series, except the second and third premolars* 

 These present strong exterior ribs between thfe eolumns, and weak ones 

 TDetween on the third molar. These teeth present no extra lobes, tuber- 



