Douglass : Fossil Horses. 2G9 



valley of the tooth between the metaloph and the hypostyle. The 

 hypostyle is simply a thickening of the posterior cingulum. 



Measurements. — Antero-posterior diameter of crown 13.3 mm., 

 transverse diameter 18 mm., length of protoloph 12.2 mm., length of 

 metaloph 12 mm., height of hypocone 8.1 mm. 



Specimen No. 1623 (Plate LXV, fig. 4) probably belongs to this 

 species. It is a third upper molar, therefore its transverse diameter is 

 not so great as that of the type. The crotchet in the present specimen 

 is not so large and there is no conule in the posterior valley. 



No. 1633 (Plate LXV, fig. 1) is a portion of a mandible with two 

 teeth in position. On account of the size and height of these teeth it is 

 assumed that the specimen belongs to the species now under consider- 

 ation. The antero-posterior diameter of the two teeth is 26 mm. 

 The height is 9 mm. The cingula on the outer faces of the teeth are 

 continuous but not heavy. The metaconid and metastylid are begin- 

 ning to separate. Another lower tooth (No. 1634) has the same 

 characters as the teeth just described. 



Mesohippus hypostylus ? Osborn. 

 (Plate LXV, figs. 7-9.) 



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

 (1904), Art. XIII, p. 170, fig. 2. 



I include provisionally in this species three upper teeth, Nos. 1625, 

 1630, and 1 63 1, also a portion of a mandible with nearly complete 

 molar-premolar series (No. 1635 Cam. Mus. Cat. Vert. Fossils) from 

 the Lower White River beds on Pipestone Creek in Montana. All 

 the teeth are considerably larger than those of the type of Mesohippus 

 hypostylus and it is doubtful if they belong to the same species. 



No. 1625 (Plate LXV, figs. 7 and 8) is a right upper molar. Its 

 antero-posterior diameter is 14.5 mm., its transverse diameter 17 mm., 

 and the height of the protocone, though worn, 8 mm. The ectoloph 

 and cross-crests are moderately oblique. The protoloph is connected, 

 apparently in part by the cingulum, with the parastyle. The proto- 

 conule is large and is plainly distinguished from the protocone. The 

 metaloph is much narrower than the protoloph, and there is only a 

 slight constriction to distinguish the metaconule from the metacone. 

 The metaconule or the outer portion of the metaloph is broad and not 

 connected with the ectoloph at the top. There is no internal cingulum 

 on the tooth. The hypostyle is small. 



