extent to that in front of it, which is twice as wide as the one in front of 

 the first premolar. The first and second premolars have but one root, 

 while the two others have two. The first superior premolar is close to the 

 canine, and has but one root ; it is separated by a diastema from the second. 

 The latter has one root, and is near the third, which has two roots. The 

 third and fourth superior premolars have each one compressed external, 

 and one internal lobe. That of the third is lower and is pressed against 

 the external. It is continued as a ridge posteriorly, enclosing a shallow 

 basin with the external tubercle. 



The true molars of both jaws have the intermediate tubercles well de- 

 veloped. The external tubercles of the superior molars are not flattened, 

 and have a low cingulum surrounding their bases. Surface of enamel 

 nearly smooth. Length of true molar series of upper jaw, M. .046 ; of last 

 superior molar, .017; width of do., .013. Diameter of first true molar, — 

 anteroposterior, .012; transverse, .011. Length of posterior three pre- 

 molars along base, .038; of diastema, .011. Length from inferior canine 

 to third inferior premolar, .028; length of diastema anterior to second pre- 

 molar, .008; do. of diastema posterior to second premolar, .007. 



This is the species I formerly called Palceocliaii'us condoni* Marsh (Plaly- 

 gonus Marsh). That species belongs to the Loup Fork fauna, and not to 

 the present one. Some teeth which probably pertain to it in Prof. Con- 

 don's collection, exhibit the peculiarity of not possessing any basal cingula 

 on the molars of either jaw. 



From the fact that Pomelf implies that some of the species of Pakeochce- 

 rus present a diastema, I have referred the Thinoliyus of Marsh to it as a 

 synonym. | Pomel's genus was, however, established on a species (P. typus) 

 which has no diastema, hence Thinoliyus is probably to be preserved. 



This species is about the size of the Thinoliyus lenius of Marsh, and 

 agrees with his descriptions in several respects. There appears, however, 

 to be a material difference between the specimens in the relations of the in- 

 ferior premolars. Marsh describes a much more considerable diastema in 

 front of the first premolar, and does not mention the N one behind the second 

 premolar. I am acquainted with a second species of the genus of about the 

 same size, in which there are but two diastemata, viz., one before and one 

 behind the first premolar, and I suppose this one to resemble the T. lentus. 

 Specimens of this character are in my collection, and I have seen one in 

 that of Prof. Condon. 

 Pal/eochcerus sub^equans, sp. nov. 



This suilline is represented by an entire cranium which was discovered 

 by Prof. Condon. It indicates a species of the size of the D&otyles tor- 

 quatus, and smaller than the Thinoliyus trichamus. 



The first true molar is not disproportionately smaller than the third ; and 

 there is a distinct cingulum at the external base of the superior true molars. 



* Rnll. U. S. Geo!. Rurv. Terrs., 1879, V, p. 5S. 

 t Catal. Vertebr. Foss. Basin Loire, lHo% p. .S6. 

 % Bull. U. S. G3nl. Surv. Terrs., 1S79, V, p. 41. 



