UPPER CRETACEOUS MARSUPIALIA 127 



The chief differences from Ectocouodon are in the relative development of the 

 various styles. A and B are distinct and quite separate, B being the larger. D and B 

 are about equal and are smaller than the pa or me. D is less conical than in Ectocouo- 

 don or Thlaeodon, and is elongated parallel to the edge. E is somewhat smaller. The 

 most prominent outer cusp is median, cone-like, and rises from the cingulum shelf 

 about halfway between the pa-me line and the outer border. It may be homologous with 

 the very much smaller cusp in this region in Ectocouodon. 



Didelphodont'me incertae sedis 

 "Superior molars, D" Osborn 1893 



This tj-pe of upper molar is represented in the American Museum by Nos. 2221 

 and 2222 and in the Yale Museum by Nos. 13660 and 13661. The pr is higher than pa 

 or me. PI and ml are close to the pa and me and their sharp median edges, unlike those 

 of Pediomys, meet in a point. In the basin internal to this point are several small 

 radiating ridges. Pa and me are about equal in size and are blunt. The external cingu- 

 lum is narrow posteriorly but forms a spur anteriorly. From the circumstance that this 

 spur is certainly anterior, it follows that these teeth are posterior upper molars, M*. 

 They probably belong to the Didelf/iodon-T/daeodon-Ectoconodon group. 



B. LOWER JAWS AND TEETH 



Under this heading come two groups, closely related zoologically but quite dis- 

 tinct in the approach which they demand. On the one hand are two good lower jaws of 

 Eodel-phis from the Belly River of Alberta, one of Euangelistes from the Lance of 

 Wyoming, and one of Proteodidelfhys from the Variegated Sandstones (Areniscas 

 abigarradas, gres bigarres, Proteodidelfhys beds of Ameghino) of Patagonia— the 

 only positively identifiable South American mammal for which a pre-Tertiary age is 

 at all probable. On the other hand are the numerous isolated teeth and small fragments 

 of lower jaws from the Wyoming Lance. The former are amenable to the usual meth- 

 ods of paleontological revision and will be treated first. In dealing with the fragmen- 

 tary Lance remains the more distinctive of the various morphological types of didel- 

 phid lower molars are described, but names are applied only to those which had 

 already been named by Marsh. To attempt to name them all would serve no useful 

 purpose at this time, and correlation with the upper molars described above is quite 

 impossible at present. 



Eodelphis Matthew 1 9 1 6 

 1916. Eodel-phis. Matthew, Bui. Amer. Mus. Nat. Hist., XXV, 482. 



Definition.— Three lower incisors, the second enlarged, the others minute. No 

 postcanine diastema. Anterior part of jaw deep and short. Trigonids of moderate 

 height, wider than long, protoconid about equal in height to paraconid, metaconid 

 smaller. 



