DAKOTA AND NEBRASKA. 



185 



The upper deciduous true molar resembles the permanent true molars, but with 

 the inner part of its crown proportionately less well-developed. 



The upper last deciduous premolar has a fore and aft elongated trihedral crown, 

 with a transverse pair of conical lobes posteriorly and a single larger pjnramidal lobe 

 anteriorly. 



The lower deciduous true molar, as in the correspondmg tooth of recent suilUne 

 animals, differs from the permanent true molars in the possession of an additional 

 transverse pair of lobes to the crown. 



The enamel of the deciduous teeth is thinner and smoother than that of the per- 

 manent set. 



Notice of specimens forming the basis of the ahooe description. — 1. The greater part 

 of the skull, including portions of the lower jaw, of a young animal. The specimen 

 formed part of the collection of Dr. David Dale Owen, from the Mauvaises Terres, 

 and is now preserved in the Museum of the Smithsonian Institution. It is repre- 

 sented in plates viii, ix, figures 1, 2, and plate x, figures 1 — -7, of the Ancient Fauna 

 of Nebraska. 



The upper jaw of the specimen contains in functional position the last deciduous 

 premolar, the true molar of the same series, and the following two permanent molars. 

 Concealed within the jaw are the last two permanent premolars and the last perma- 

 nent true molar. Portions of the lower jaw contain in functional position the last 

 temporary molar and the following two permanent true molars. Concealed withm 

 the sam.e fragments are the last permanent premolar and the last permanent true 

 molar. 



The supra-occipital and the ex-occipitals are yet separate, l^ut the latter and the 

 basi-occipital are co-ossified. The latter, and the basi- and pre-sphenoids, are also 

 separated. 



Measurements of the specimen are as follow : 



Estimated length of the skull, about 

 Estimated length of the lower jaw, about . 

 Length of sagittal crest, partially estimated. 

 Length of temporal fossa along the middle, . 

 Greatest breadth of cranium at the parietals, 

 Breadth of skull at back part of the zygomata, 

 Length of zygomatic fossa, . 

 Breadth of zygomatic fossa posteriorly, 

 Depth of zygoma just back of the orbit, 

 Breadth of forehead at fronto-malar sutures, 



24 



Inches. 



16 

 12 



4 



41 



21 



S3 



3J 



23 



2i 



61 



