Diameters M. I 



1881.] 161 [Cope. 



is absolutely quite elevated above the alveolar border. Its summit presents 

 a V externally, and there is a small posterior median angle. In the last 

 true molar this angle is a little more prominent than in the others, and 

 rises into a cusp. The external bases of the crowns are protuberant, but 

 there are no cingula. Enamel smooth. 



The ramus is rather compressed, and the masseteric fossa is well marked, 

 and is bounded anteriorly by a prominent rib. 



Measurements. M. 



Length of true molars , . .0100 



/ anteroposterior . 0035 



Diameters M. Ill } vertical .0035 



' transverse. 0080 



anteroposterior .0035 



transverse 0028 



Depth of ramus at M. II .0070 



This species is smaller in all dimensions than I. didelphoides, and the 

 crowns of the molar teeth are shorter and more elevated than in that 

 species. 

 Deltatherium absarok^e Cope. American Naturalist, 1881, p. 669. 

 A small species, represented by an imperfect cranium and lower jaw 

 with nearly complete dentition. 

 Stypolophus aculeatus Cope. 



Several fragmentary mandibles nearly coincide in measurements with 

 this species. The molars are .0240 in length, and the ramus is .0140 in 

 depth. The only difference in the measurements is that the true molars 

 measure .0250 in 8. aculeatus. The latter is, however, a species of the 

 'Bridger epoch, so that further comparison will be necessary before identi- 

 fication is made. 



Stypolophus whiti^e, sp. nov. 



Stypolophus strenuus Cope. Bulletin U. S. Geol. Survey, vi, 192 ; not 

 of Report Capt. Wheeler, vol. iv, pt. ii. 



The greater part of the skeleton, with skull and dentition of this species, 

 were brought from the Big-Horn by Mr. Wortman. A part of a mandible 

 of a second individual was also found. The species is, however, primarily 

 based on a specimen from the "Wind river. This is represented by a right 

 mandibular ramus which supports 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 inter- 

 mediate between the 8. breviealearatus and 8. strenuus in proportions. It 

 has not the rudimental heels of the molars of the former species, nor the 

 robustness of the latter. 



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



