VERTEBRATES FAUNA OF THE LOtJP FORK BEDS. 27 



orbital fossa. There is an oval maxillo-nasal fossa, which is strongly pro- 

 nounced. The infraorbital foramen issues above the middle of the first 

 true molar. The maxillary bone projects about half the diameter of the 

 last molar tooth posteriorly to it, but this dimension may increase a little, 

 as the animal is not fully grown. The anterior orbital border marks a 

 point above the middle of the last superior molar. The last superior 

 molar is just protruding from the alveolus. The first and second molars 

 are worn. Their crowns have a greater anteroposterior than transverse 

 diameter, and the section of the protoeone is greater longitudinally than 

 transversely, although its junctiou with the paraconule is complete. The 

 enamel of the lake borders is simple, except that that of the posterior 

 wall of the anterior lake presents the usual loops well defined. The su- 

 perior molars have the crowns long and well curved transversely. In the 

 inferior molars the anterior and joosterior lobes of the metaconid have 

 but little anteroposterior extent, and the paraconid and hypostylid are 

 well developed. The column of the last inferior molar, which forms 

 the heel, is quite small. 



Measwements . 



Mm. 



Length of maxillary bone to anterior border of P. m. i 127 



Length of ditto from orbit to preorbital foramen 64 



Anteroposterior diameter of true molars 84 



Diameter of crown of M. i i anteroposterior 28 



I transverse 25 



Length of crown of inferior true molars 88 



Length of crown of last inferior molar 30 



Diameters of M.i J anteroposterior 31 



I transverse 13 



Depth of ramus at front of M.i 46 



Depth of ramus at posterior end of M. iii 67 



Found by myself in the Loup Fork bed of Donley count}'^, Texas. Mr. 

 W. F. Cummins found the nearly complete skull of a colt at the same 

 locality in which the above cranium was found, which from the character 

 of its facial region and the dimensions of its teeth I can only refer to this 

 species. 



In its general form the skull exhibits the character of immaturity in the 

 relatively large size of the brain ease and orbits, and contraction of the 

 muzzle and occiput and zygomatic foramina. The profile of the brain case 

 is convex, descending rapidly posteriorly to the occiput. There is a feeble 

 sagittal ridge originating from feeble, posteriorly converging temporal 

 ridges. The sagittal ridge becomes a crest, and immediately divides into 

 two lateral occipital ridges or rather angles, which include between them 

 a triangular space with a doubly convex posterior margin, the inion. This 

 heart-shaped area is longer than wide instead of wider than long, as in 

 adult animals. The occiput is low, and has a median vertical angle, on 



