15 Bulletin American Museum of Natural History. [Vol. XXXIV, 
codus. The variations in size are considerable and there are numerous 
intergradations in relative antero-posterior width of the upper teeth, so that 
the specimens cannot readily be sorted out into well-defined groups. As in 
Phenacodus practically no progressive premolar development is shown in 
this genus. At least four species, indicated by size and relative proportions 
of teeth, are recognizable. . 
Ectocion osbornianum Cope, 1882. 
Oligotomus osbornianus Corn, 1882, Pal. Bull., No. 34, p. 182; Ectocion, 1882 
(May 20) Amer. Nat., p. 522; LE. osbornianum, 1885, Tertiary Vertebrata, p. 696, 
pl. xxve, figs. 1, 10; 1887, Amer. Nat., p. 1061, fig. 25. 
L'ype, Amer. Mus. Cope Coll. No. 4409, upper and lower jaw fragments; 
Gray Bull beds, Bighorn basin, Wyo. J. L. Wortman, 1881. 
Distinctive characters. Ps-ms = 39, m3 = 24.2: ps not longer antero- 
posteriorly than ps, simple, with protoconid and high posterior basal cusp. 
I reter to this species about twenty-five specimens from the Gray Bull 
and about as many each from the Sand Coulee and Clark Fork beds. The 
widest differences between the specimens so referred is in the relative length 
and width of the upper molars. The type represents the condition of least 
antero-posterior compression of the teeth and there are gradual stages 
between this and a condition where the compression is very marked. The 
lack of good series of upper and lower teeth in association makes it difficult 
to determine if more than one species is represented here. The extremes 
of each condition occur in each horizon although the type with compressed 
molars is the most prevalent in the lowest beds. 
Ectocion superstes sp. nov. 
. Type, No. 233A, a series of lower teeth, P3s-mg, left side, with lower 
canine; Lost Cabin beds, Wind River basin, Wyo. J. L. Wortman, 1891. 
Distinctive Characters. Ps-ms = 42.5, m3 = 25.5 Ds longer antero- 
posteriorly than p, and with a tendency for a cusp to split off from the ante- 
rior ridge of the protoconid; highly developed entoconid on ps. 
_ This type is the only specimen of the genus in the collection coming 
from a level higher than the Gray Bull, and shows in the premolars a very 
slight progressiveness over the lower beds forms. The pg is rather more 
molariform in general appearance than in other species, due largely to the 
reduction of the ridge which curves forward and inward from the protoconid, 
