288 F: B. Loomis — On Ticholeptus Rusticus and 



behind, in both the premolars are more crowded than in 

 AgTiochcerus and less crowded than in Oreodon. Pro- 

 toreodon has the more closely set premolars and the outer 

 crescents of the molars less concave, and the nngnals are 

 neither laterally compressed as for claws, nor broadly de- 

 pressed as in some of the later oreodonts. In Protagrio- 

 chcerus the teeth are less closely set, the molars have the 

 crescents more concave, and the nngnals are nnknown. 

 Hyomeryx represents a side line in which there is a ten- 

 dency to lose the incisors of the npper set. 



In the Oligocene, Agriochoeras is clearly set off as an 

 independently developing family, by the feet developing 

 claws, by a wide gap behind the canine before the premo- 

 lars begin, by the f onrth premolar above becoming molari- 

 f orm, and by the great concavity of the onter crescents of 

 the npper molars. The genns is abundant and continues 

 clear though the Oligocene running into a dozen larger 

 and smaller species. Oreodon is a very abundant genus 

 though with rather few species, 0. culbersoni and 0. gra- 

 cilis being the most abundant. The manus retains digit 

 1 as a vestigial toe, certainly in 0. culbersoni and 0. gra- 

 cilis, and this is the basis for the separation of Oreodon 

 and Eporeodon. Two types of skulls very like each other 

 are found but in 0. culbertsoni the bulla is small; while 

 the other form, otherwise very like this, has a large and 

 inflated bulla. This inflated bulla is the basis of the genus 

 Eucrotaphus with E. jacksoni as the type. Whether this 

 is sufficient basis for a genus is doubtful but I should let 

 it stand for the present until a study of the skeleton of 

 Eucrotaphus jacksoni is made. That may show other 

 characters justifying the genus and there must be mate- 

 rial for the study though I have not found it. Whether 

 E. jacksoni had the first digit of the manus retained or not 

 is not known. In the development of the bulla it is more 

 like Eporeodon than is Oreodon. These two genera as 

 known today run through the Lower and Upper Oligocene. 

 From the dwarf fauna found at Pipe Stone Springs, Mom 

 tana,Douglass described two other genera of Lower Oligo- 

 cene oreodonts, Limnenetes based on a skull which shows 

 the orbit open behind ; and so far as known this may well 

 represent Protoreodon continuing on into the Oligocene : 

 and Bathygenus based on a fragment of a lower jaw. 

 This latter genus needs much more complete material in 

 order to establish its independence and position. In the 



