28 GEOLOGICAL SURVKY OF TEXAS. 



each side of which it is concave, the superior part of each concavity being 

 horizontal from the overhanging of tlieinion. The occipital condyles are 

 remarkahl}' small. The z3'gomatic foramen is onl^' about one-fourth as 

 wide as the interorbital space^ The superior orbital border is very promi- 

 nent anteriorlj^ and is deeply openly emarginate posteriorly. The an- 

 terosuperior protuberance is bounded by a notch of the anterior orbital 

 border. There is no malomaxillary angle, nor preorbital fossa; There 

 is, on the other hand, a very large nasomaxillary fossa, with a rather 

 abrupt inferior border, which rises anteriorly to a point above tlie in-* 

 fraorbital foramen. It is separated anteriorly by a narrow bony isthmus 

 from a deep but small premaxillary fossa. Extremities of the nasal and 

 premaxillary bones broken off. The infraorbital foramen issues above 

 the anterior part of the penultimate deciduous molar. 



The mastoid and basioccipital elements have fallen out, leaving clean 

 the sutural surfaces of the squamosal and exoccipital. From the appear- 

 ance of the latter it seems that basioccipital has no share in the composi- 

 tion of the condyles. The petrosal, as in the genus Equus, is divided 

 into two parts by a horizontal suture. The inferior portion is more pro- 

 duced infer iorly than in the horse and quagga, presenting an angular 

 ridge downward, which runs forwards and inwards and sends off a trans- 

 verse branch posteriori 3\ The tympanic is separated from it bj^ a groove, 

 and diverges outwards and backwards from the postglenoid process, with 

 which it is in contact at the interior extremity. The postglenoid process 

 has considerable transverse extent, and its free border is directed down- 

 wards and inwards, but it is not produced into a process at this point, as 

 in the Protohippus mirahilis and the Equi. The maxillary bone is pro- 

 duced posterior to the last molar about the length of the latter, and pre- 

 sents an obtuse angle into the zygomatic foramen. An angle of the first 

 permanent molar is visible at a fracture. The palatal notch extends to op- 

 posite the metacone of the second molar. 



The cusps and crests of the teeth are more acute than in the unworn 

 teeth of the permanent dentition. The internal cusps are connected with 

 the external cusps by oblique crests, which terminate opposite the ridges 

 which form the anterior boundaries of the paracone and metacone. The 

 metaconule is continuous with the hypocone in all of the molars, while the 

 paraconule is swollen anteriorly, so as to make an emargination witli the 

 protocone in front. The trihedral hypoconule is large and isolated. It 

 is concave posteriorly in the first and third molars. The parastylid of 

 the first molar is larger than in the others and is more produced ante- 

 riorly, as in the permanent dentition. It sends a strong cingulum in- 

 wards along the anterior margin of the crown to the anterior base of the 

 protocone. In this tooth the metaconule sends a process towards the par- 

 aconule, which it does not reach hy a wide interval. This process is 



