344 
AETIODACTYLA. 
American fauna indicates the absence there of the conditions which caused 
their extermination from North America. 
Pliauchenia humphresiana, Cope. 
- Plate Ixxvii, fig. 4. 
Proc. Phil. Acad., 1875, p. 258; Ann. Kept. Chief of Engineers, 1875, ii, p. 989. 
The animal now described is of about the size of the Procameliis occi¬ 
dentalism or somewhat larger than any of the existing Llamas. The mandible 
is stout and deep, contracting rapidly forward. The canine and first pre¬ 
molar are especially stout, and separated by a very short diastema; that 
separating the first and third premolars is also short, being less than that 
which separates the first and second in Procamelus occidentalis. Could it be 
supposed that the second premolar is abnormally absent from the P. Immphre- 
siana, the diastema would be reduced to a very small compass. Without 
this supposition, the diastemata, both before and behind the first premolar, 
are shorter than in any of the PTOcamcl% as P. rohustuSm P. angustidens, P. 
Jieterodontus, and P. gracilis. The mental foramen issues below the anterior 
border of the first or cuniform premolar, and the anterior border of the 
latter marks the posterior margin of the symphyseal suture. The third pre¬ 
molar is nearly as long as, but narrower than, the fourth, and the true 
molars increase rapidly in size posteriorly. 
Measurements. 
Leugth of the dental series from the front of the canine to the front of the last 
molar...... 
M. 
0.125 
Length from the canine to the first premolar. 
Long diameter of the first premolar.. 
Diastema to the third preraolar. 
Length of the third premolar. 
Length of the first true molar.. 
Width of the crown of the first true molar.... 
Length of the crown of the second true molar 
0. 010 
0. 010 
0. 023 
0.011 
0.019 
0.011 
0. 025 
This species is dedicated to Brig. Gen. A. A. Humphreys, Chief of En¬ 
gineers, U, S. A., in recognition of the enlightened interest in’ all depart¬ 
ments of scientific investigation exhibited in his long and able administra¬ 
tion. 
