92 AMERICAN MESOZOIC MAMMALIA 



by two curved transverse furrows, one running from the notch between pr"* and me'' on 

 the main transverse ridge down into the basin and up to the notch between the pr"" and 

 the posteroexternal cusp, and the other from the notch between the me'^ and the postero- 

 internal cusp into the basin and up the internal slope of the posteroexternal cusp. Three 

 grooves run from near the tip of the pr'' posteriorly and a little internally until they 

 meet the first of the transverse talonid furrows. The minor features of this pattern are 

 quickly obliterated by wear, but at least traces of the pattern can always be seen. 



Anterior to Ms the molars become progressively narrower relative to their length 

 and also decrease slightly in absolute height and length. M7-8 were progressively 

 smaller than Ms-e- The most anterior molars are so narrow that the internal cusps 

 appear much like so many elevations of an internal cingulum plastered on the higher 

 external cusps. 



Mandible 



The horizontal ramus is slender, the alveolar border nearly straight, the lower 

 border gently convex, with its greatest depth below M5. The single mental foramen is 

 beneath the anterior root of Ps. The symphysis is not very clear in this species, but 

 seems to have extended back as far as the last premolar. Coronoid, condylar, and 

 angular processes are distinct and well marked." The former is large, high, and long. 

 Its edges are not thickened and it is flat and plate-like. Anteriorly it arises at an angle 

 of about 60° to the alveolar border, and it originally extended back as far as does the 

 condyle, from which it was separated by a small notch. The latter is pedunculate and 

 is somewhat lower than in Laolestes. The articular surface looks backward and but 

 little upward and is slightly elongate transversely. 



The external face of the jaw back of the alveolar portion is slightly excavated, but 

 there is no distinct masseteric fossa. A slight convexity passes posteriorly to the con- 

 dyle. The angular process, below this, is concave externally, but its lower border is 

 thickened. The internal aspect of this region is like that of D. striatus, where it is more 

 clearly displayed. 



Measurements of Type 



Lengths : 



C Pi P2 P3 P4 Ml Mo M3 M4 Ms Me 



1.5 0.9 0.8 1.2 1.3 1.4 1.7 2.0 2.1 2.1 2.0 

 Depth of ramus below M4, inside, 4.1 mm. 



^^ Since it was studied by Marsh and before the present research the type mandible was removed 

 from the matrix. The posterior portion was cracked in many places before this, and in clearing it the 

 pieces were all retained, but their relationships very slightly altered. By carefully washing the surface 

 and checking against a good X-ray photograph it has been possible to avoid erroneous impressions from 

 this source, but these changes should be kept in mind in studying photographs. The coronoid now appears 

 too slender and low, the supracondylar notch too large, and the curvature of the horizontal ramus too 

 great (due to a median break repaired with plaster some of which remains between the two broken 

 surfaces) . 



