JAB Bulletin American Museum of Natural History. [Vol. XXXIV, 
of the maxilla is preserved, but it is a character of Ectocion, as also is the 
development of metacone and mesostyle on m’, but the p® and the m' and 
m2 are decidedly Phenacodus and not KEctocion. I hesitate to establish a 
new species for this single specimen, especially since no identifiable speci- 
men of P. brachypternus showing the anterior premolars is present for 
comparison and the relative size of the m® is too variable in this genus, 
although it appears to be more constant in this species than in others. 
It is very possible also that the two-rooted condition of the p! is not an 
unvarying character within specific limits. 
Measurements of No. 16249. 
mm 
LMG cic ueecb este Werseib 4c tei wueerie Ver ier ore Tate aie ar Glee tie uke wit de Sen yotete ody ail 51 
In? transverse Giamerer oss. a oD 
me? amtero-pesterior diameter... 02. 6... oss oon ws Ps 
mé . De ay ete eine ts acre hase 6. 
m® transverse Bet way eo Carden cane See os 8.2 
Be en eiie gig) aoe aie be Wie ss Noe aes a0. 
p® antero-posterior 2 sy ae eto eect Raa NG Ce ree. 
p*® transverse Me a a 7. etc OO: 
Epeeacedue astutus (Cope), 1875. 
Opisthotomus astutus Corr, 1875, cee Cat. Vert. Eoc. i. hex... p.. 16; 0. 
astutus 1877, Ext. Vert. N. Mex., p. 152, pl. xlv, fig. 9. 
Type, a first or second lower molar associated with a premolar tooth; 
from the Wasatch of New Mexico. E. D. Cope, 1874. Type lost. 
The molar is, without question, that of a small species.of Phenacodus 
but the premolar, which was mistaken by Cope for a last lower molar, and 
which formed the principal characters of the genus Opisthotomus, cannot 
be identified from the figure with any degree of satisfaction. The closest 
resemblance, shown in the inner view of the tooth, is to a fourth lower 
premolar of Phenacodus with reduced metaconid. The molar agrees in 
length, according to Cope’s measurements, with the first or second molar 
of P. brachypternus but is slightly broader transversely. The premolar is of 
a size which might be associated with the molar but shows less wear than 
would be expected. Cope states that the two teeth were found in close 
association. Assuming that the association is correct and that no topotype 
can be selected, it seems best to let this species name stand for this speci- 
men only rather than to refer other types and specimens to it, based on 
comparison with the molar tooth only. 
