THE LOWER EMBAR OF WYOMING 649 



thick, thinning rapidly outward from the summit of the arch on 

 the posterior edge, and not quite so abruptly about the middle of 

 the anterior edge. The anterior edge is turned downward at the 

 outer end, giving to the end a twisted appearance, without causing 

 it to be greatly recurved. A broad depression runs from the outer 

 end to the inner at about the middle of the tooth. At the outer 

 end this depression is very shallow and has no well-defined bounding 

 ridge in front. The entire coronal surface is marked by rather 

 strong, subequally spaced, transverse undulations, three to six of 

 which are unusually deep in front of the top of the arch. In most 

 specimens wear has reduced the surface until the deep undulations 

 are the only ones remaining, and in some specimens the undulations 

 seem never to have been very pronounced. 



No tooth from the Embar agrees perfectly with the figures and 

 descriptions of the type of D. propinquus, but the similarity is 

 striking. Unfortunately the type of maxillary tooth of this species 

 could not be found and the identifications had to be made entirely 

 from figures and descriptions. D. mercurii and D. powellii were 

 described from mandibular teeth only. 



The mandibular teeth are broad and short, thick at the broad 

 end and thinning rapidly toward the narrow end; they are strongly 

 arched longitudinally along the anterior edge but gently curved 

 to nearly straight along the posterior edge; the narrow end is 

 curved to form a semicircle, but this is preserved in only one speci- 

 men. The teeth are divided into anterior and posterior parts by 

 a furrow that runs from the outer to the inner end at about one- 

 third of the width from the posterior edge. The furrow is broad 

 and shallow at the outer end and narrows to a deep groove near the 

 inner end. The part in front of the furrow is much elevated, and 

 in the middle is crossed by two to four transverse grooves that often 

 become deep pits on the front edge of the furrow and do not cross 

 the hinder ridge. The outer end has no hinder ridge, but back of 

 the middle a ridge becomes prominent and a sharp narrow part of 

 it borders the furrow. The most perfect teeth show the origin of 

 this posterior ridge. Originally it seems to have been a thin, flat, 

 winglike expansion, which later doubled back on itself for 1 cm. 

 and crumpled up at the place where the fold occurred. In some 



