210 0. C. Marsh—New Tertiary Mammals. 
low tubercle, which is separated by a deep notch from the an- 
terior elevated portion. ‘The latter is ae of three pointed 
cones, the front one being the highe 
Measurements. 
Space occupied by last two lower molars,...........+++- a 
Antero-posterior diameter of last lower molar, Cae ise eris 18 
PR URUNVOTUR CRRIOROT, Fes vs ince es cence sib es och es eases 11 
Depth of jaw below ‘last lower MROIRE 5. tc ck eee 3°5 
The specimen here described was a last September, by 
the writer, near Henry’s Fork, Wyomi 
Part III. 
Nearly all the remains briefly described in this section of the 
present communication belonged to quite small animals, many 
of them insectivorous, and several evidently marsupials. In 
the complete description, now in course of preparation, these 
various species will be fully described, and their more exact 
affinities determined. 
Stenacodon rarus, gen. et sp. nov. 
A new Feevont of very small mammals, apparently related dis- 
tantly to Hyopsodus, may be established on a single last t lower 
molar, in good reservation which is one of the rarities of our 
collections. The crown of the tooth is remarkably narrow. It 
is composed omsaritially of four main cusps, nearly of the same 
size, and a larger posterior tubercle. The main cusps are al 
ranged in two transverse foe and the posterior pair are the 
highest. There is no basal ridge. The species was somewhat 
smaller than Hyopsodus paulus Leidy. 
Measurements. 
maathe siig diameter of last lower molar,.......-+++ 65™ 
Transverse diameter through anterior pair of cones,...--+ 2°9 
Piadavors diameter through posterior tubercle,.....++++ 2° 
Height of posterior pair of cones above jaw,...------ ‘wee 
The above erage was found by the writer, last autumn, 
near Henry’s Fork. 
Antiacodon venustus, gen. et sp. nov. 
This species, which is about the same size as Homacodon i 
gans, is at present represented only by part of a lower jaw, wit 
the characteristic lower molar, so often alone preserved. The ¢ 
crown of the present je has a similar composition to that 0 
the same molar in Homacodon. The four principal cones stat 
in nearly opposite pairs, but the posterior tubercle is less widely 
