278 THE rUERCO FAUNA. 



weakness of the posterior inner tubercle, and in the absence of the ear-like 

 expansion of the external angles. 



The number of possible combinations of tubercular and tubercular- 

 sectorial molar teeth is considerable, and many of them are represented in 

 the genera of the Creodonta. Deltatherium is a genus which has, in the 

 lower jaw, two tubercular sectorials, and a third with a long heel posterior 

 to them. The genus thus stands between Stypolophus and Dkhjmictis, but is 

 nearer the former than the latter, since it has three true molars. It differs 

 further from both in having but three premolars and a wide diastema. The 

 canine is well developed. Although there is a tubercular tooth, the cutting 

 apparatus is well developed, and indicates more than usually rapacious 

 habits. There is as yet but one species known. It is allied to Leptktis, and 

 agrees with Mops and Mesodectes in possessing an internal tubercle of the 

 third superior premolar, but differs from both in having but one external 

 cusp of the fourth superior premolar, resembling in this respect the more 

 typical Oxyanidce. 



With this genus we enter a series of forms in which the dentition is 

 more decidedly opossum-like than in those previously considered. Besides 

 Beltatherimn there are species of the Eocene which I have referred to the 

 Miocene genera Ictops and Perafherium, and there are the as yet purely 

 Miocene genera Leptictis and Mesodectes. The Eocene Diacodon must be 

 referred to the same category. Leptictis differs from DidcJphijs in having 

 but two superior incisors on each side instead of four; Ictops bicuspis has 

 three on each side. Diacodon differs in not having the anterior inner cusp 

 of Didelphys, and in Ictops it is present, but small. This character will serve 

 to distinguish these genera empirically from Stypolophus, as will also the 

 development of cusps on the heels of the molars. 



Deltatherilwi fundaminis Cope. 



American Naturalist, 1H«0, March, p. 3S8. Lipodfctes penetrans Cope 1. c. 18?1, p. 1019. 

 Plates XXIII p, figs. 8-11; XXV a, fig. 10; XXV .1, fig. 3. 



Represented by specimens which display the dentition of both max- 

 illary bones minus the canines, and l>y several mandibles. The most 

 instructive specimen includes the cranium anterior to the sagittal crest with. 



