142 
MESODONTA. 
adapted in size to the T. tutum, and I have no hesitation in describing them 
together. 
In the mandibular ramus in question, the canine alveolus is small and 
has a nearly vertical direction. That of the first premolar is smaller and 
vertical. The second has left two roots. The third is compressed, but stout, 
and has a broad but very short heel behind. It has no cingulum, and the 
anterior border of the crown rises nearly vertically from its base. The 
fourth premolar has three cusps and a wide heel. The principal cusp is 
external; at the inner side of its anterior base is a small one, and a little 
behind its middle on the inner side is one of intermediate size, the two 
apices separated by a notch. The heel is without tubercles, but hAs a short, 
low, submedian ridge. There is a faint cingulum on the external side of the 
heel. The first premolar has three anterior cusps standing close together, 
and a wide posterior crown. The three anterior cusps are connected by 
yokes, of which the anterior is convex. The posterior part of the crown is 
concave, and is not surrounded entirely by an elevated ridge. It is bounded 
on the external side by a V-shaped ridge, whose limbs extend, the one to 
the posterior of the two interior anterior cusps, the other to the middle of 
the crown behind, the angle rising into a low cusp. On the inner side, a 
low ridge extends from the inner cusp mentioned, and terminates in a low 
cusp at the posterior third of the inner side. There is a continuous cingu¬ 
lum on the external base of the crown, and the enamel is smooth. 
As compared with the T. jarrovii, this species is distinct in the form of 
the first true molar tooth. In that species, the posterior basin is completely 
surrounded by a raised border, as in the succeeding molars; in this one, it 
resembles a premolar in having the posterior cusps unconnected with each 
other. It is also materially smaller than in T. jarrovii. 
Measurements. 
M. 
Length of the bases of the molars from the first to the fifth inclusive. 0. 0205 
Length of the last premolar... 0. 0055 
Width behind. 0. 0040 
Elevation anteriorly.. 0. 0045 
Length of the croivn of the first true molar... 0. 0050 
W idth of the same anteriorly... 0. 0035 
Width of the same posteriorly.. 0. 0045 
