scott: toxodonta OF THE SANTA CRUZ beds. 
127 
The milk-premolars are, generally speaking, molariform, with some dif- 
ferences, especially in the anterior ones. The first (dp 1 ) is so early shed 
and replaced, that it is difficult to find examples of it and I have seen no 
unworn specimens. As ordinarily found, it has a small subquadrate crown, 
with two external lobes, and an enamel-lake on the grinding surface, the 
remnant of the internal valley. The second (dp—) is much larger in both 
diameters and has two equal external lobes, each with a prominent median 
rib. The valley is T-shaped, directed longitudinally, with a narrow, slit- 
like opening on the inner side ; three small spurs invade the valley, two 
from the posterior and one from the external wall. Posterior to the main 
valley is a fossette, with three small, circular pits in its floor, which, on 
abrasion, give rise to three minute lakes, a character of the permanent 
premolars. The special peculiarity of this tooth, in addition to the 
presence of the posterior fossette and its pits, is the large size and anterior 
prolongation of the postero-internal cusp (tetartocone), which extends for- 
ward almost to a contact with the antero-internal (deuterocone). 
The third milk-premolar (dp—) is still larger than dp-, especially in the 
antero-posterior diameter, and is almost exactly like a molar, except for 
the presence of a prominent median rib on the antero-external lobe. The 
fourth (dp-) is the largest of the temporary series and, like dp-, has a 
median rib on the antero-external lobe, but it is less prominent' ; otherwise 
it is like a molar. Dp- and - are set en Echelon, like the true molars, the 
antero-external angle of each overlapping the preceding tooth. 
B. Lower Jaw . — The incisors are broad, scalpriform teeth, which in- 
crease in size from di T to dig and, when freshly erupted, with a median 
ridge on the postero-superior face ; when worn and rooted, di T has con- 
siderable resemblance to a human incisor. These teeth are thin and an- 
tero-posteriorly compressed and di x and x are much less distinctly tri- 
hedral than their permanent successors : dig does not become a tusk, but 
develops a root and ceases growth very early, and is abraded at the tip 
like the other incisors, not obliquely truncated as is i x . All the milk-in- 
cisors are somewhat procumbent, but less decidedly so than the perma- 
nent ones, and each one at first extensively overlaps the tooth in front of 
and internal to it, but in older stages this overlapping is much reduced, 
as the crowns are narrowed by wear. The canine is in close juxtaposi- 
tion to di ¥ , which it somewhat resembles in form, but is very much 
smaller. 
