0. 0. Marsh—American Jurassic Mammals. BBs: 
In Ctenacodon, the mental foramen is large, and situated 
below the middle of the diastema. The dental foramen is 
under the last molar, but its entrance is partially concealed by 
a ridge descending from the base of the tooth to the inflected 
border of the angle. | 
In none of the specimens of Ctenacodon preserved is there 
any trace of a mylohyoid groove. 
Ctenacodon potens, sp. nov. 
A third species of Ctenacodon, much larger than C. serratus, 
is represented by several jaws and isolated teeth, discovered 
since the first species was described. The most important of 
these specimens, which may be taken as the-type, is the right 
upper jaw represented in Plate VIII, figures 2 and 3. The 
lower jaw with incisor, figured on the same Plate, may also be 
referred to this species. A second lower jaw in better preser- 
vation, but without the incisor, may likewise be included, 
although somewhat larger in size. 
The upper jaw above mentioned agrees in its general shape 
with that of Ad/odon. It indicates a short, broad skull, with 
strong, expanded, zygomatic arches. There is a small antorbital 
foramen, as in Al/odon. The four premolars present increase 
in size from before backward. The first and second are of the 
Allodon type. The last two have strong marks of attrition on 
the inner surface of their crowns, as shown in figure 2, of the 
same Plate. They differ from the corresponding teeth in 
Allodon, in being more compressed, and adapted to cutting.* 
There were apparently two true molars, which are wanting in 
the present specimen, but their position and size are similar to 
those of the same teeth in Adlodon. 
The left lower jaw represented in figures 7, 8, and 9 shows 
that the incisor in this species was very large in size, and a- 
most effective weapon. It grew from a persistent pulp, and 
its massive base extended back under the fourth premolar. 
The crown is oval in outline at the margin of the jaw, some- 
what more compressed above, and sharply pointed at the 
apex. There is a shallow groove on the outer surface of the 
lower half of the crown, and a corresponding depression along 
the middle of its inner face. A careful examination shows no 
signs of wear on any part of the crown. 
The premolars are separated from the incisor by a long dias- 
tema, The first premolar is small, without serrations, and is 
placed close to the second. The latter is larger, inserted by 
two fangs, and has the summit faintly notched. The third 
premolar was still larger, but is so much fractured in the 
* A somewhat similar tooth of Microlestes is figured by Owen in Mesozoic 
Mammals, Plate I, fig. 16. 
