298 ON THE EXTINCT MAMMALIA OF 



the two teeth in question would have had about the same antero-posterior diameter 

 as in the full and older series. 



2. Figures 6, 7, plate XVII, represent two mutilated upper molars from Bijou 

 Hill, originally supposed to belong to Hlpparion speciosum, but, from comparison with 

 additional material, are now viewed as pertaining to Merychippus insignis. They 

 apparently belonged to the same individual, and agree in proportions with the corres- 

 ponding teeth above described, but are less worn than those of the full series from the 

 Niobrara River. 



One of the specimens, figure 6, a first molar, has the central lakes conjoined, and 

 both are filled with cementum, unlike the condition observed in the Niobrara fossil. 

 The anterior lake, as in the latter, opens into the internal oblique valley of the 

 crown. The other specimen, figure 7, a fourth or fifth molar, is irregularly worn, as 

 is not unfrequently observed in old Horses in the domestic state. The inner columns, 

 in this tooth, have lost their distinctive characters, and the bottoms of the valleys 

 defining them appear on the triturating surface as islets. 



Xhe measurements of the specimens, partially estimated, are as follow : 



Length externally, . . . . 



Length internally, .... 



Antero-posterior diameter, 

 Transverse diameter, .... 



The late Dr. Samuel Moore submitted to my inspection three specimens of isolated 

 upper molar teeth, from Washington Co., Texas, which appear to be referable to 

 Merychippus insignis. The locality was previously mentioned as one from which a 

 molar tooth of Hipparion speciosum was obtained. The specimens were picked up 

 from the surface of the ground, and have no adherent matrix. Two appear somewhat 

 smoothly water-worn at the root ; the other has minute lichens attached. They are 

 as follow : 



1. A first superior molar, about half worn, and broken at its fore part. It is repre- 

 sented in figure 53, plate XVIII, and agrees closely in proportions and anatomical 

 character with that of the entire series above described, except that its central lakes 

 are filled with cementum. 



2. A second or third superior molar, but slightly worn, represented in figure 52. 

 It agrees in its proportions with the corresponding teeth of the above described sei'ies. 

 A narrow tract of dentine has become exposed almost continuously along the summits 

 of the constituent lobes, including the internal ones. 



superior molar. 



4th. 



Lines. 



Lines 



. 5* 



5i 



. 3 



2 



. 11 



8i 



. 9 



9i 



