270 Annals of the Carnegie Museum. 



No. 1 63 1 is a second upper premolar. The antero-external style is 

 not large. The antero-external cusp is quite large but there is no 

 outer tubercle on the protoloph. The posterior external tubercle on 

 the metaloph is well developed. There is a large hypostyle and it is 

 connected by wear with the postero-internal cusp. The anteropos- 

 terior diameter is 15 mm. and the transverse diameter 15 mm. 



No. 1635 (Plate LXV, fig. 9) is a portion of a mandible with all 

 the cheek-teeth except part of the last molar. Because of the size and 

 height of the teeth it is provisionally associated with the upper teeth 

 described above. The length of the molar-premolar series, exclusive 

 of M3, is 70 mm. The length of M T is 15 mm. and the height of the 

 protoconid is 9 mm. The teeth are high for a species from the Lower 

 White River horizon. P T is small. There are prominent external 

 cingula on all the teeth except the first premolar. There is a tendency 

 toward a separation of the metastylid from the metaconid but this is 

 not shown by an inner groove. The entostylid is quite well developed. 



Mesohippus bairdi (Leidy). 



Palceotherhwi bairdi Leidy. Proceedings of the Academy of Natural 

 Sciences, Philadelphia, Vol. V, 1850, p. 122. 



The anterior portion of a skull containing the molar-premolar series 

 of both sides, was found below the middle of the nodular beds (Middle 

 White River) on White Butte in Billings County, North Dakota. The 

 specimen is No. 1644 of the Carnegie Museum Collection of Verte- 

 brate Fossils. The teeth are extremely brachyodont for a horse from 

 this horizon — more so than any specimens I have seen from the Lower 

 White River beds of Montana. By the pattern of the teeth they could 

 hardly be distinguished from those usually considered as belonging to 

 Mesohippics bairdi, though I have not access to the type of that species. 

 The preorbital fossa is quite large and deep, making the top of the 

 muzzle narrow. 



Upper White River Beds. 



Mesohippus brae hy sty lus ? Osborn. 

 ( Plate LXV, figures 5 and 6. ) 

 Bulletin of the American Museum of Natural History, Vol. XX, 

 1904, Art. XIII, p. 175, fig. 6. 



I include provisionally in this species Nos. 1639, 1641, and 1643 

 (Cam. Mus. Cat. Vert. Foss. ). They consist of teeth which were 



