POEBROTHERIUM. 23 



but is longest or most prominent at the middle, is convex externally, and sloping 

 plane internally, and is inserted in the jaw by two diverging fangs. 



Inferior Molars. — (Figs. 1, 4.) The lower teeth, preserved in the specimen, consist 

 of the permanent true molars, and the three temporary molars. The former are re- 

 markable for the simplicity of their lobes, and these, as in the case of those aboye, 

 have not as prominent summits as are found in the Musks. The internal surface of 

 their inner lobes is vertical and plane in comparison with what it is in the Musks 

 and other ruminants, and its longitudinal ridges are but slightly elevated above 

 the intervening spaces. The external surface of these lobes is quite plane and 

 nearly parallel with the internal. 



The outer lobes are vertically prismoid Avith the anterior surface broader than 

 the posterior, and the internal surface more vertical than in the Musks or Deer. 

 The extremities of the crescentic summits join the corresponding margins of the 

 inner lobes, and there is no disposition to the bifurcation of the posterior horn of 

 the antero-external lobes as in the Musks. 



Each transverse pair of lobes, in the specimen, presents a trilateral pit of enamel 

 surrounded by a narrow tract of exposed dentine. 



The fifth lobe of the last molar is a simple, thin, enamelled plate, with a trench- 

 ant edge. 



The last temporary molar, as in all ruminants, is composed of three pairs of 

 lobes ; but, in the specimen, from the obliteration of the interlobular enamel pits, 

 it rather consists of three antero-posterior prismoid lobes. 



The two temporary premolars, in the broad trenchant character of their crown, 

 resemble those of the Musks. Their trenchant margin rises to the middle of the 

 teeth, the external surface is elevated into three slight convexities, and the inner 

 surface is convex posteriorly, but is depressed anteriorly. The margin of the second 

 premolar is broadest posteriorly, and is worn off in this position in the specimen, 

 and the anterior fifth of the tooth bends within that preceding it. As before ob- 

 served, when the specimen was first received, a fragment of the first permanent 

 premolar remained in the lower jaw, situated about five lines in advance of the 

 first temporary molar. 



This species is named in honor ©f Dr. Thomas B. Wilson, of Philadelphia, a 



distinguished patron of the natural sciences. 



MEASUREMENTS. 



Inches. Lines. 



Distance from meatus auditorius to anterior part of first permanent premolar . 4 9 



Distance from meatus auditorius to infra-orbital foramen .... 3 1 



Diameter of orbit from lower part of post-orbital arch to lachrymal margin . 1 2 



Breadth at meatus auditorius .....••■• J- " 



Breadth at auditory bulla .......••■-' 1 



Breadth at malar bone below orbit ....•••• ^ ■* 



Breadth at infra-orbitar foramen ......•••! ^ 



Breadth above first permanent premolar .....•• Ti 



Breadth above middle true molar .....-•• 1 1" 



Height of orbit from base of lower jaw ....... 1 8 



Height of lower jaw at condyle ......■• 1 H 



Height of lower jaw at middle true molar ....... 7 



