SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 
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The first premolar is a small, single-rooted tooth, with compressed- 
conical crown, but is complicated by a narrow valley on the posterior side, 
enclosed between two ridges which run down from the apex of the crown. 
The remaining lower premolars (p2, 3, t) have essentially the pattern of 
the molars, with some differences, but develop roots at a much earlier 
stage and therefore have less decidedly hypsodont crowns. On the ex- 
ternal side is a vertical groove, running down to the base of the crown 
and dividing it into two lobes, which are of crescentic form, with valleys 
on the inner side, giving the bicrescentic pattern so very frequent among 
primitive ungulates of many different groups. These internal valleys, 
however, are shallow and have but small vertical extension and are soon 
obliterated by wear. The second premolar, the simplest of the last three, 
has imperfectly formed crescents, especially the anterior one, and there is no 
spur, or pillar, in the posterior crescent. On the external face, the groove 
is broad and open and the two lobes are of nearly equal size. In the 
third premolar the external valley is a narrow groove, and the posterior 
lobe is distinctly larger than the anterior ; the posterior horn of the anterior 
crescent projects obliquely backward as a spur and encloses a deep fossa 
with a prominent spur in the valley of the posterior crescent, and there is 
also a deep pit in the posterior valley. At a very early stage of wear, 
even before the eruption of pT, the inner opening of both these pits is 
obliterated and the pits are converted into small enamel lakes. The 
fourth premolar is like the third, but the posterior lobe exceeds the anterior 
in size to a greater degree, though much less than in the molars. 
The lower molars increase progressively in size from mi to nn, the pre- 
dominance of the latter growing more marked with age, as in the case of 
the corresponding upper tooth, but even more strikingly. These teeth 
are all decidedly hypsodont and do not form roots until the animal is 
beginning to grow old. They have the bicrescentic pattern already 
described in the premolars, but the difference in size between the two 
lobes is much greater than in the premolars, the posterior crescent being 
far larger than the anterior, and the disproportion attains its maximum 
in mi. The valleys on the inner side of the crescents have a much 
greater vertical extent than in the premolars and the posterior valley 
much more than the anterior. The spur in the posterior valley is sepa- 
rated by a deep cleft from the hinder horn of the anterior crescent and is 
itself marked by a deep pit and there is a similar, but larger and deeper, 
