• CREODONTA. 311 



DiDYMICTIS PROTENUS CoPE. 



Plate XXV d, figs. 4,5. 



System. Cat. Vert. Eocene New Mexico, U. S. Geog. Survs. W. of 100 M., 1875, p. 11. Report upon 

 U. S. Geog. Survs. of W. 100 M. In charge of First Lieut. Geo. M. Wheeler, Corps of Engi- 

 neers, U. S. Army, under the direction of Brig. Gen. A. A. Humphreys, Chief of Engineers 

 U. S. Army ; Part II, Vol. IV, Paleontology, 1877, p. 123. Washington. Paleontological Bulletin 

 No. 34, p. 159, Feb. 20, 1882. 



Jaws, more or less complete, of six individuals from the Big Horn 

 basin, are referable to this species. They agree closely in measurements 

 and belong to the larger variety of the species figured on Plate XXXIX of 

 the report to Captain Wheeler. 



A left maxillary bone containing the last four molars furnishes the best 

 characters for this part of both genus and species yet obtained. The third 

 premolar has no interior lobe, but the inner base is more convex than the 

 external, and has a low cingulum. There is a short posterior heel, and a 

 shorter anterior basal tubercle. The fourth premolar has three external lobes, 

 and an internal conic lobe which is opposite to the space between the ante- 

 rior and middle external lobes. The anterior external lobe is the smallest 

 and is subconical. The middle lobe is a flattened cone with a three-sided 

 base. The third lobe is a blade directed outwards as well as backwards. 

 Its free edge forms, with the posterior edge of the middle lobe, a sectorial 

 blade divided by a median fissure. The first true molar is triangular, with 

 the longest side anterior and the external and posterior sides equal. The 

 external side is very oblique, subtending an obtuse angle with the posterior 

 ide. It is also concave medially, and the anterior lobe projects outwards 

 and forwards. The two external cusps are small, conic, well separated, and 

 situated much inside of the external border. The internal cusp is large, 

 and is separated from the externals by a small triangular tubercle on each 

 border of the crown. Each of the latter descends into a cingulum which 

 extends outwards. A strong cingulum surrounds the internal base of the 

 crown, disappearing at the intermediate tubercles mentioned. The second 

 true molar is much smaller than the first, and the details of its structure are 

 the same. The anterior exterior angle is not so much produced. 



The fourth premolar is as effective a sectorial tooth as that of the spe- 



