EE SE a | pie alli SS Bes, ete La 
O. C. Marsh—New Jurassic Mammals. 397 
The symphysis is short, and the two rami were not firmly 
codssified. The lower dental series is as follows: 
Incisors 1-1; premolars 4-4; molars 2-2. 
The incisor was large, and had a compressed base. The pre- 
molars are wedge-shaped, and all have sharp trenchant crowns. 
The summit of each is very thin, and the last is distinctly 
serrated. The first lower molar had a low crown, very similar 
to that of Plagiaulaz. 
The following are the principal dimensions of this specimen : 
Length of portion preserved ....--.------------ blue 
Space occupied by lower teeth ..-..------.----- 8°5 
Space occupied by four premolars ....--.------- 45 
Depth of jaw below first premolar. ----.-------- 2°5 
Depth of jaw below last premolar .--. ---------- 3°5 
Height of crown of last premolar ---- ----------- 15 
A second specimen, also a right lower jaw, agrees essentially 
with the one here described. Both are from the same locality, 
in the Atlantosaurus beds of Wyoming. These fossils, with 
those of the genus Plagiaulax, belong to a well marked family, 
which may appropriately be termed Plagiaulacide. 
Dryolestes arcuatus, sp. nov. 
A third species of Dryolestes is at present represented by five 
Specimens, two upper, and three lower jaws. This species 
appear to have been arranged on a curve opposite to that of 
the upper molars. : 
The principal measurements of the type specimen are as 
follows: 
Space occupied by teeth in maxillary -- --------- es 
Space occupied by six posterior molars ---- ----- ig 
Height of maxillary above second premolar- .---- 5 
Space occupied by first three upper molars------- 3°5 
Tinodon robustus, sp. nov. 
A species of this genus, about twice as large as the one 
previously described (7. bellus), is indicated by a lower Jaw with 
