212 O. C. Marsh—New Tertiary Mammals. 
This unique specimen was discovered, in September of last 
year, near Henry’s Fork, by Mr. F. Mead, Jr., of the Yale party. 
Mesacodon speciosus, gen. et sp. nov. 
This species and genus is based essentially on a nearly per- 
fect lower jaw, with most of the teeth in good preservation. In 
its general features, the jaw resembles that of Limnotherium, and 
the molars are similar in composition to those of J. elegans, 
although considerably narrower. The teeth form a continuous 
series. e canine is large and compressed, and almost in con- 
tact with the s earn There are three premolars, and three 
true molars. The first premolar had but a single fan e 
timate. e jaw is short, twisted longitudinally, and was not 
covssified with its fellow. The lower border was produced 
posteriorly, and the angle inflected. The remains indicate an 
animal about the size of the preceding species, and probably 
insectivorous. 
Measurements. 
Longitudinal extent of six lower molars,............++: 203. 
Extent of three lower true molars,..............-.- BP - 
Pn ee pamgaia! of last lower PROSE, cies 5 ep ts 4°3 
AYORENCTOR IAIDONOE 65 oy hak oat a ee ths 5s ech = te 3° 
Depth = ou on Toner face below last lower molar,... 7° 
The jaw described above was —— by the writer, ‘as Sep- 
eciban = Grizzly Buttes, Wyoming. 
Hemiacodon gracilis, gen. et sp. 1 : 
A genus of small mammals, apparently insecivorows with 
molar teeth resembling those in Mesacodon, is well re resented 
by portions of several lower jaws, and possibly By other char- 
e same species, 
witohi somewhat smaller than that last described. ‘The 
lower ‘ain preaented are rather slender and’ compressed. The 
teeth form a continuous series, os the dental formula appears 
to be as follows: Incisors 2, canine 1, premolars 3, and molars 
3. There were a Te two ‘aeall incisors, and the ae 
e jaws were not codssified at the symp trie The lower 
margin was produced epee and the angle inflected. 
easurements. 
oe extent of nine eed MD ce cet ea 20° = 
Extent of premolar and molar series,..........-.-++++-172 
Extent of iemEe Sesese ook” 
