Marsh Collection, Peabody Museum. 33 



rior cusp ; the heel is little developed, and there is a faint 

 indication of a cingulum in front. 



The premolar in advance of this, which is really the second 

 according to the proper enumeration, has a single fang dis- 

 tinctly smaller than that of the canine. The two incisors, as 

 determined by their alveoli, were also smaller than the canine, 

 and had an erect position as in the monkeys, not procumbent as 

 in the lemurs. In one specimen, the first is shown to be a 

 little larger than the second, as in some monkeys. The 

 mandibular rami were never coossified. 



.Description of the Type of Palceacodon vagus. 



Of the upper teeth, the molars, figure 123, alone are known, 

 if my determination that those of P. vagus refer to Omomys 

 Carteri is correct. From what has just been said, I think 

 there can be little doubt of this. The first molar is the largest 

 of the series, and its more or less rectangular crown is made up 

 of three principal cusps arranged in the form of a triangle, of 

 which two are external and one is internal. The external cusps 

 are imperfectly conical, slightly flattened on the outside, and 

 connected with the internal by two distinct ridges (the trigonal 

 ridges), upon which near the middle are developed two small, 

 indistinct, intermediate cusps. The large internal cusp is imper- 

 fectly Y-shaped, and around the inner side of its base there is 

 a strong cingulum. Posterior and internal to this cusp, the 

 cingulum develops a considerable swelling, which is the begin- 

 ning of the posterior internal cusp of the higher monkeys. It 

 is built out in such a way as to give a decidedly rectangular 

 appearance to this part of the outline of the crown. This 

 aspect is augmented by the unusual development of the 

 cingulum at the antero-internal angle, where it likewise devel- 

 ops a small, though distinct cusp. In the second molar, which 

 is slightly smaller than the first, the structure of the crown, as 

 well as the arrangement of the cusps, is essentially the same. 

 The postero-internal cusp is, however, not so well developed, 

 and the internal outline of the crown is more rounded and less 

 angular than that of the first molar. The last upper molar is 

 reduced to about the same degree as that of the lower jaw. 

 The intermediates of this tooth are very indistinct, and the 

 internal cingulum is little developed. The inner part of the 

 crown is narrower and more pointed. 



The premolars are unknown, but in the type specimen the 

 fangs of the fourth are to be seen. These consist, of two 

 external and one internal, as in the molars. Of the two 

 external roots, the posterior seems to be the smaller. 



The vertical range of this species is great, and specimens 

 occur from the lowest to the highest levels of the beds. 



[To be continued.] 



Am. Jour. Scl— Fourth Series, Vol. XYII, No. 9*7. — January, 1904. 

 3 



