650 E. B. BRANSON 



specimens the upper part lies on the lower without having become 

 cemented to it, while in others the evidence of folding is lacking. 

 Behind this ridge there is, in some cases, a short, shallow, longi- 

 tudinal depression. The entire coronal surface is marked by sub- 

 equally spaced transverse undulations that are often indistinct. 



The foregoing description refers to the large teeth. The smaller 

 teeth lack the conspicuous posterior ridge and the strong transverse 

 undulations, and the longitudinal furrow is less pronounced. 



Fig. 10 of PI. V shows the undulations very well, but no good 

 specimen shows them distinctly enough over the entire surface 

 to permit of their being brought out in a photograph, though 

 they are readily traceable on the teeth themselves. The presence 

 of the strong undulations suggests the formation of the large teeth 

 by the union of several smaller teeth, but the older teeth have much 

 the stronger undulations, unless they are reduced by wear, and the 

 small teeth are nearly smooth. 



Comparison with the type of the maxillary tooth, which is pre- 

 served in the Illinois State Museum, discloses some differences. The 

 Wyoming teeth are larger and thicker compared to other dimen- 

 sions. The Illinois specimen has subequal longitudinal ridges which 

 are lacking in the Wyoming form. The surface of the Illinois form 

 is marked by a sort of reticulate, threadlike network which is not 

 present in the Wyoming specimens ; but there is only one specimen 

 of the Illinois form and there are many of the Wyoming. Speci- 

 mens no larger than the type are in the collection, but they are 

 proportionately thicker. Some specimens show irregular and dis- 

 continuous longitudinal ridges. The network on the Illinois 

 specimen is preserved where the tooth is not worn, and all of the 

 Wyoming specimens are worn. 



I am inclined to think that the Wyoming maxillary teeth are 

 not specifically identical with the Illinois form, and I also think 

 that St. John and Worthen's types of mandibular and maxillary 

 teeth from Illinois are not conspecific. The Wyoming and Illinois 

 mandibular teeth seem to belong to the same species. 



Comparison with the type of D. merciirii discloses very close 

 agreement. The transverse grooves are inconspicuous on account 

 of wear and the small size of the specimens, but the location of the 

 grooves is easily made out. 



