E. L. Troxell — Amynodonts in Marsh Collection, 25 



of South Dakota in 1889 by Professor Marsh; only 

 recently has it been freed from the stony matrix and 

 identified. 



Skull characters. — The malar-temporal suture begins in 

 the orbit; the zygomatic arch is concave internally in 

 both directions and is very broad. The strong sagittal 

 crest rises an inch or more above the cranium. The 

 posterior nares lie entirely behind the last molar, with 

 the opening very deep and well guarded by the broad 

 pterygoids. The wide spacious articular glenoid surface 

 extends onto the heavy postglenoid process, which curves 

 forward and away from the paramastoid to which it is 

 closely joined. The basicranial angle is large, a progres- 

 sive character. The roof of the mouth is arched into a 

 deep fossa between the premolars. There are deep cheek 

 depressions, but they are restricted in area. The nasal 

 bones are short. 



W274- TYPE 



Fig, 1. — Metamynodon rex, sp. nov. Holotype. Side view of skull of the 

 ponderous aquatic rhinoceros. Note heavy zygomatic arch, deep facial pit, 

 strong outward curving canine (restored), and short face. X l/^- 



Dentition. — The incisor teeth, absent here, are known to 

 be small in the type of M. planifrons. A diastema of 

 3 mm. separates the canine from P^. P^ is obsolete. P^ 

 forms an irregular pentagon; it is probably three-rooted, 

 and is made up of crests and ridges like the other premo- 

 lars, but appears in its natural posture to have been 

 rotated through an angle of 80 or 90 degrees ; thus the 

 protoloph and metaloph extend directly backward instead 

 of transversely. 



P^ is broad transversely and short antero-posteriorly, 

 the diameters being 31 by 21 mm. The ectoloph is broad 

 and in the present state of wear occupies about half of the 



