Scott and Osborn.] ^^^ [Sept. 2, 



Hyracodon. The rest of the dentition shows no particular deviation from 

 the usual type, nor are important differences from the Bridger species 

 observable in the skeleton, except perhaps a slight reduction in the rela- 

 tive size of the lateral digits. In size this species about equals H. agra- 

 rius. 



Prothyracodon intermedium, gen. et sp. nov. — This very interesting type 

 is apparently intermediate between Hyrachyus and Hyracodon. The 

 type specimen consists of a fragment of the superior maxillary contain- 

 ing the fourth premolar and second molar in place, with the alveolus of 

 the first molar. As in Hyrachyus the premolar has but a single internal 

 cusp and two transverse crests enclosing a valley. The external cusps are 

 like those of Hyracodon, the outer wall of the crown being nearly flat and 

 suhquadrate in outline ; the two constituent cusps are but faintly indicated, 

 but are somewhat more pronounced than in Hyracodon. An antero-ex- 

 ternal buttress or fold of the cingulum is present, as in both the Bridger 

 and White River genera. 



The second molar is essentially the same as in Hyracodon ; the antero- 

 external lobe is much more reduced than in Hyrachyus, and the transverse 

 crests directed more obliquely inwards and backwards ; but on the other 

 hand, the projection from the anterior crest into the median valley which 

 is to be seen on all the molars of Hyracodon is here wanting. 



The present species is quite small ; it is about the size of Hyracliyus 

 agrarius. 



Measurements. 



M. 



Fourth upper premolar, anteroposterior diameter 010 



" " " transverse " 014 



Second upper molar, antero-posterior diameter 016 



" " " transverse " 0175 



Isectolophus annectens, gen et sp. nov. — This genus is closely allied to 

 Helaletes of the Bridger, but its dentition is one step nearer to that of the 

 tapir. In Helaletes the antero- external cusp of the upper molars is less 

 reduced and there is less difference between that and the postero- external 

 cusp, than in Hyrachyus. This tooth structure would almost suffice to 

 remove Helaletes from the Lophiodontido} as defined by Cope. In Isectolo- 

 phus this equality of the external cusps is still better marked, and, more 

 important still, the external wall is extended behind the posterior pillar 

 just as in the tapir, so that this pillar becomes a median thickening of the 

 posteroexternal cusp, instead of being a thickening of the posterior edge 

 of that cusp, as in Hyrachyus and Helaletes. The first and second upper 

 molars are thus almost exactly like those of the tapir ; the transverse 

 crests are low and thick, and a strong cingulum surrounds the crown. 

 The premolars are probably all simpler than the molars ; at all events 

 this is true of the third. The lower molars are like those of Helaletes, and 

 the last one has a well-developed heel or third crest ; there seems, how- 



