74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



for this in the more hmited and generally more fragmentary remains 

 of Hyracothenum at other horizons and localities in the Wasatch is 

 not so easily demonstrated. I am convinced that two forms are repre- 

 sented in the rather striking size range for Wasatch materials now 

 allocated to H. vasac dense, but there is the practical matter of sepa- 

 rating them in horizons other than at La Barge or Dad (Kitts, 1956, 

 p. 49), because the modes thus postulated would no doubt shift with 

 time. It may be noted that in the smaller as well as the larger of the 

 two La Barge forms included under H. vasacciense P^ is progressive, 

 as Kitts has defined this species. In plate 13, figures 4 and 9 might 

 be interpreted as representing the smaller form. 



Nearly 200 specimens from the La Barge horizon in Sublette County 

 are now referred to H. vasacciense. Of this number more than a 

 third are in a size range that was earlier included under H. index. 

 The smaller specimens are relatively fewer in the Dad fauna, and in 

 the New Fork only 2 of the 33 specimens of Hyracotherium are small 

 enough to have been included in H. index. However, 10 out of this 

 total are thought, for the most part on the basis of size, to represent 

 H. craspedotum. A shift in modes for the New Fork species may 

 also be involved. A somewhat different distribution is noted for the 

 Cathedral Bluffs although only five specimens are known. Three of 

 these are of a size that would have included them with H. index. 

 The other two are referred to H. craspedotum. Incidentally, none has 

 characters that would justify their inclusion in Orohippus. The upper 

 molar associated with P.U. No. 161 11 shows no evidence of a 

 mesostyle. 



HYRACOTHERIUM, cf. CRASPEDOTUM Cope 



(Plate 13, figure 11) 



Essentially, the specimens from the Knight that I had tentatively 

 assigned to Hyracotherium venticolum are those which Kitts (1956, 

 p. 53) regards as representing H. craspedotum. These are for the 

 most part strikingly large specimens, but rather few in number, that 

 seemed beyond the limit for H. vasacciense. In two instances, how- 

 ever, maxillary portions are known in which P^ is of the type described 

 by Kitts as characterizing H. craspedotum. One of these, P.U. 

 No. 161 73, from Fossil Butte was particularly mentioned by both 

 Kitts (1956, p. 53) and me (as H. venticolum, 1956, p. 66) ; and the 

 other is from the Cathedral Bluffs (U.S.N.M. No. 22497; see pi. 13, 

 fig. 11). A second specimen from Cathedral BlufTs is a lower jaw 

 (P.U. field No. 326W) in which the combined length of M2 and M3 is 



