DAKOTA AND NEBRASKA. 303 



The superior molars have short square crowns, devoid of cementum, and are in- 

 serted into the jaw, when functionally used, by fangs. The crowns are composed of 

 an external pair of derai-conoidal lobes, an internal pair of conical lobes, and a median 

 pair of smaller lobes, which usually appear as prominent folds continuous with the 

 inner lobes and curving outwardly in advance of the external lobes. At the back 

 part of the crown, in the interval of the contiguous internal and external lobes, there 

 exists a large crescentoid tubercle springing from the basal ridge, which with slight 

 interruptions surrounds the crown. 



The inferior molars, as in the case of the upper ones, have short crowns, devoid of 

 cementum, and are inserted into the jaw by fangs. The crowns are oblong-square, 

 and are composed of an external pair of crescentoid demi-conoidal lobes, and an inter- 

 nal pair of smaller conoidal lobes, which present more or less disposition to become 

 twin lobes, and which are homologous with the inner twin columns in the lower 

 molars of the Equidce. In the first molar an additional lobe is developed at the fore 

 part of the tooth, and is attended with a reduction in size of the antero-external lobe. 

 In the last molar there is an additional posterior lobe homologous with the crescent- 

 oid demi-conoidal lobes in advance. 



To the family of Anchitlieridce belong the genera Anchitherium, Eypoliippiis, 

 Anchi2ypus, and Parahipims. 



ANCHITHERIUM. 



In the superior molars of this genus the external lobes are the best developed, and 

 the median ones the least. The median lobes appear as thick ridges bulging slightly 

 at their inner part, where they are continuous with the internal conical lobes. The 

 latter are somewhat compressed from before backward, so that their transverse diame- 

 ter is greater than the antero-posterior. In the inferior molars the antero-internal 

 conical lobe, develop)ed at and conjoining the contiguous horns of the external lobes, 

 is feebly indented at the summit. 



Anchitherium Bairdi. 



The remains of a species of Anchitherium, to which the above name has been 

 applied, are rather abundant in the Mauvaises Terres miocene d'eposits of White 

 River, Dakota, belonging to the intermediate beds B, C, D, of Dr. Hayden's section. 

 The greater portion of half a dozen skulls, together with many fragments of jaws with 

 teeth, isolated teeth, and fragments of other bones, are contained in the diflerent col- 

 lections of fossils I have had the opportunity of examining. 



The best specimen of a skull is represented in plate XX of the present memoir, and 



