18^9.] 45o [Cope. 



species of Protohippus. The postorbital process turns its edge outwards. 

 The external extremity of the glenoid cavity is quite prominent. The 

 posttympanic process is sliort and acute. The palatine foramina are 

 opposite the posterior edge of the first true molar. The supraorbital fora- 

 men is large and distinct. The infraorbital foramen issues above the 

 middle of the fourth premolar. The palate is as narrow as in //. calama- 

 rium, but the premolar teeth are narrower ; the greatest transverse diame- 

 ter of the second premolar in H. isoneaum is two-thirds that of the palate 

 between them while it is equal in H. calamarium. 



Measurements of Skull. 



M. 



Length from incisors to occipital condyles :^28 



" " to glenoid surface (axial) 257 



" " to end of OS maxillare 210 



" " to p.m. iv (axial) 068 



" " to canine " 037 



Transverse diameter of orbit 044 



"Width at paroccipital processes 0;i4 



" between first true molars 044 



" " second premolars 030 



" at diastema near p.m. iv 028 



Long diameter p. m. iv 013 



Diameters p.m. iii i 



^ I tra 



anteroposterior 024 



ransverse (at column) 014 



T^. , . (anteroposterior 019 



Diameters m. i. . -^ ' 



transverse 019 



Long diameter of crown of I. i 013 



The only virtebra of this individual, which is well preserved, is an atlas. 

 This one has the general proportions of that of the horse, but diflers ma- 

 terially in the less anterior extent of the transverse process. This does 

 not, as in the horse, enclose the anterior arterial foramen, which is there- 

 fore represented by a notch. The hypapophysis is well marked, and the 

 condyloid cavity deeply notched on the external side. The first dorsal is 

 strongly opisthocoelous, its ball is subquadrate. There is a strong ob- 

 tuse hypapophysial ridge. The anterior capitular articulation is large 

 and flat. 



The last two lumbars are preserved somewhat injured. They are 

 united mutually and with the first sacral by rather large articular surfaces 

 of the diapophyses. The penultimate has an obtuse hypapophysial keel, 

 which is less distinct in the last one. 



Measurements. 



M. 



Length of atlas on side 052 



Expanse of atlas transversely 086 



Width of canal behind 033 



