172 
RODENTIA. 
Plesiarctomys delicatissimus, Leidy. 
Plate xliv, figs. 9 and 12. 
Paramys rlelicatissimus, Leidy, Proc. Acad. Phila., 1871, p. 231; Eeport U. S. Geol. 
Surv. Terrs., i, p. Ill, pi. vi, figs. 28-29. 
I obtained a portion of a mandibular ramus of one individual, which 
agrees in measurements and other characters with the species above named. 
The jaw supports the second and third molars, and a considerable portion 
of the incisor. An isolated incisor of another animal of this species is 
figured on the same plate (q. v.). 
The ramus is compressed, and not robust in its proportions, although 
deep in proportion to its length. The diastema is short, and the mental 
foramen is just below the anterior border of the first molar. The masseteric 
fossa extends to the line of the posterior border of the third molar. The 
four tubercles which distinguish the molars of this genus are here elevations 
of the border of the crown, and they inclose a large basin. The anterior 
inner is the highest. 
Measurements. 
Leugth of the three antei’ior molars. 
Length of the third molar. ... . __ 
Width of the same... 
Length of the first molar.. 
Width of the same. 
Depth of the ramus at the second molar. 
S fi'i^tero-posterior. 
Diameter ot the incisor< ^ 
i transverse. 
M. 
0. 0100 
0. 0030 
0.0020 
0. 0038 
0. 002G 
0. 0094 
0. 0033 
0. 0020 
These measurements show the difference in size between this animal 
and the P. buccatus. 
Plesiarctomys delicatior, Leidy. 
Plate xliv^, figs. 10-11. 
Paramys delicatior^ Leidy, Proc. Acad. Phila., 1871, 231; Leidy, Eeport U. S. Geol. 
Surv. Terrs., 1873, i, p. 110, pi. vi, 26, 27; pi. xxvii, 16, 18. 
Two mandibular rami indicate that this species was a member of the 
Wasatch fauna of New Mexico. They are more robust than those of the 
P. delicatissimus^ the incisor teeth are wider, and the tubercles of the molar 
teeth more strongly pronounced. The opposite pairs of tubercles are more 
or less connected by low ridges, a point especially marked in the anterior 
