292 TUE WASATCH AND UKlDdEU FAUX^. 



the type of the genus, S. pungens. The molars have the general characters 

 of the con-esponding ones of that species, but differ in their greater eleva- 

 tion in comparison with their length, and the greater convexhy of the outer 

 side. The shortness is occasioned by the abbreviation of the heel, which, 

 in the last molar present, is very small and flat, and without keel or tuber- 

 cle on its surface. That of the molar preceding it is larger, and presents 

 in its elevated outer margin a trace of the keel seen in the smallest species, 

 but it is also of reduced size. Enamel smooth. 



M. 



Length of two molars - 016 



Length of penultimate crown 008 



Width of penultimate crown 0047 



Length of penultimate heel 002 



Stypolophus WHITI.J: Cope. 



StypolophuK atremiHo Cope, Bull. U. S. Geo). Surv. Terrs., 1861, vi, p. V)2, not of 1675. 



Plato XXV 6, figs. 8-14. 



This species is represented by a right mandibular ramus which sup- 

 ports all the molar teeth, and displays the alveolus of the canine, and lacks 

 all posterior to the coronoid process. Also by a portion of the frontal bone, 

 two vertebrae, fragments of scapula, humerus, ulna, radius, ilium, and tibia, 

 and the greater part of both tarsi They represent a species larger than the 

 Virginian opossum, and intermediate between the S. hrevicalcaratus and S. 

 strennus in proportions. It has not the rudimental heels of the molars of 

 the former species, nor the robustness of the latter. 



Tlie inferior outline of the mandible is gently curved from the canine 

 to below the last molar. The anterior border of the masseteric fossa is well 

 marked, but not the inferior border. The ramus is compressed and deep. 

 Tlie canines have stout roots and narrow curved crowns. The first pre- 

 molar is separated by a short space from the canine, and by a longer from 

 the second premolar. It has either a single compressed root or two roots 

 confluent within the alveolus. The crown is truncated obliquely behind. 

 The second premolar is two-rooted and the crown is elevated anteriorly and 

 depressed posteriorly. The third premolar is more symmetrical, but the 

 heel is produced. It is narrow and keeled mediiilly. The fourth premolar 

 is abruptly larger than the third. Its crown is simple, except a low tubercle 



