Cope.] 486 [Sept. 17, 



This observation confirms my conclusion that the Credonta form a grou\:> 

 intermediate between the Marsupialia and Carnivora. I may add that in 

 Triisodon the inferior border of the lower jaw is not inflected posteriorly. 



Char, specif. — Size about that of the wolf Inferior canine directed up- 

 wards, its section ngarly elliptic ; a faint posterior, no anterior cutting 

 edge. Fourth premolar rather large, with an anterior basal cingulum 

 which is angulate upwards, and is not continued on the inner side of the 

 crown. Cusps of the heel each sending a ridge forwards, the internal 

 lower, obtuse and descending to base of inner side of large cusp ; the ex- 

 ternal larger, with an acute anterior cutting edge continuous with the cut- 

 ting edge of the large cusp. True molars with an external, but no in- 

 ternal basal cingulum. Border of heel with one large and three smaller 

 tubercles, the former with, the latter without, anterior cutting edge. Ena- 

 mel of all the teeth nearly smooth. All the cusps are rather obtuse. 

 Measurements. — Length of inferior molar series : M. .080 ; long diameter 

 of base of canine .013 ; length of true molar series .044 ; length of base 

 of Prem. IV. .016 ; elevation of crown of do. .014 ; length of base of M. 

 II. .016 ; width of do. in front .011 ; elevation of do., .014. The measure- 

 ments of the jaw are not given, as the animal is not adult, the last molar 

 not being yet protruded. 



From the lowest Eocene beds of New Mexico. 



DELTATHERiuM FTJNDAMiNis, gen. et sp. nov. Char. Gen. Fam. Lep- 

 tictidcB, agreeing with Ictops and Wesodectes in possessing an internal tu- 

 bercle of the third superior premolar, but differing from both in having but 

 one external cusp of the fourth superior premolar. CJiar. Specif. Repre- 

 sented by the dentition of both maxillary bones minus the canines. The 

 second premolar is convex on the inner face. Tlie base of the third is a 

 nearly equilateral triangle. The bases of the true molars are triangles, 

 with the bases external. The internal angle supports an acute cusp, and 

 has a posterior basal cingulum, which is very strong in the last three mo- 

 lars. The two external cusps of the first and second molars are situated 

 well within the base, which is folded into a strong cingulum. This cingu- 

 lum develops strong anterior and posterior angles. This is the largest 

 species of the family yet discovered. Extent of series of last six molars, 

 M. .045 : of true molars .036 ; diameters of fourth premolar, anteropos- 

 terior .0074; transverse .0076 ; do. of second true molar, anteroposterior 

 ,0087; transverse .0100. This species was a fourth larger than the com- 

 mon opossum, and very much resembles it in dental characters. 



CoNORYCTES COMMA, gen. et sp. nov. Char. Oen. Allied to Mesonyx. 

 Inferior canines not rodent-like, with conic crowns. Molars 3 — 3, the first 

 one-rooted, the second two-rooted, the third Avith an anterior conic cusp 

 and a posterior grinding heel. True molars consisting of two lobes, of 

 subcylindric section, separated by deep vertical grooves. Enamel devel- 

 oped on internal and external faces of crowns. Char. Specif. Founded 

 on a mandibular ramus which lacks the last molar, and has the crowns 

 of the others worn. The external faces of the molars are much more ex- 



