TRIPLOPUS. 



687 



Triplopus amarorum Cope. 



Proceeds. Amer. Philos. Soc, 1881, p. 389. 

 Plate LV, figs. 6-9, and LVIII a, fig. 2. 



The characters of the fore foot of this species being unknown, it is not 

 possible to determine its generic position. It has, however, one of the well- 

 marked characteristics of the genus Triplopus, in the osseous inclosure of 

 the meatus auditorius externus, through the ossification of the external pro- 

 longation of the otic bulla and tympanic cartilage. I cannot, therefore, 

 refer it to HyracJiyus. 



It is represented by a skull from which a large part of both maxillary 

 bones and the maudible have been lost, and which is accompanied by parts 

 of the ulna and radius, parts of the ilium, a femur, and tibia, and nearly 

 all of the posterior foot of the right side. The postexior parts of both max- 

 illary bones remain, and they suppoi't each, the last superior molar tooth 

 from which the external wall has been broken away. The portions of mo- 

 lars remaining exhibit characters which lead me to suspect that the species 

 does not belong to Hyrachyus. The anterior cross-crest of the molar pre- 

 served, is lobate, resembling the same ridge in the species of Anchitheriuni. 

 The posterior cross-crest is uninterrupted. If this species possesses affinity 

 with Anchitherium. it will perhaps possess three digits of the man us, in which 

 case it will be referred to the Triplopidce, in harmony with the indication 

 furnished by the ear structure. 



The Triplopus amarorum is much larger than the T. cubitalis, equaling 

 the Hyracodon nehrascensis. It differs from the T. cubiialis in the stronger 

 temporal ridges and more elevated sagittal crest; also in the shorter post- 

 tympanic process. The internal lobes of the last superior molar are con- 

 nected by a basal ledge, not found in the T cubitalis. 



The interorbital space is wide and flat, and is most expanded at the 

 postorbital angles. 



From this point the face contracts rapidly forward. From the same 

 angle it contracts abruptly posteriorly to the rather narrow brain case. The 

 anterior temporal ridges ai-e nearly transverse near the postorbital jirocesses, 

 and then converge more gradually, uniting opposite the posterior inferior 

 border of the zygomatic fossa. The elevated sagittal crest diverges into 



