RIGGS: HOPLOPHONEUS OCCIDENTALIS. 4I 



surface as a common, large, anteriorly directed opening. Just 

 within their opening, however, the three diverge, forming distinct 

 canals. The posterior opening of the ali-sphenoid canal is in front 

 of, and near the oval foramen, but not included in a common 

 fissure with it as in H. robiisttis. The carotid canal is represented 

 by a groove alongside of the basi-occipital, within the optic bulla. 

 It terminates just without the posterior end of a ridge bounding 

 the median groove of the basi-occipital. Midway between this and 

 the anterior border of the occipital condyle is the expanded open- 

 ing of the re-condylar foramen. The dental foramen opens just 

 back of the anterior margin of the coronoid process, and forms a 

 groove to the base of the condyle. 



Dentition I.| C. | P. | M.i. The dentition is complete except the 

 crown of the lower incisors and canines. The upper incisors are 

 proportionally shorter and stouter than those of H. robiistiis. The 

 first and second are similar in size and shape; the third is only a 

 trifle longer, but much stouter. The canine is strong and de- 

 cidedly recurved; its margins are well rounded throughout the 

 greater part of its length, but near the point they become thinner and 

 trenchant. The posterior edge is minutely denticulate, but the 

 condition of the specimen does not show whether or not this was 

 true of the anterior edge. The third premolar is removed from 

 the canine by a wide distance. It agrees very closely, both in size 

 and shape with the corresponding tooth of H. robust us. The 

 superior sectorial has a shorter and blunter median lobe, a lower 

 heel, and a more prominent anterior secondary lobe. The tuber- 

 cular molar is two-rooted and very similar to that of H. robustus. 

 The lower incisors show quite a variation in size. The first is 

 small and compressed; the second considerably larger; the third is 

 almost as stout as the lower canine. The third lower premolar is 

 no larger than that of H. robustus. Its posterior lobe is less prom- 

 inent, the anterior one has disappeared entirely. The fourth 

 premolar is similar in every respect to Leidy's figure of the type. 

 The median lobe is shorter, and the secondary lobe less prominent 

 than in H. robustus. The lower sectorial has only a very slight 

 heel, but the postero-internal cusp is distinctly present. 



MEASUREMENTS OF SKULL. 



Smaller Larger 



Specimen. Specimen. 



mm. mm. 



Condyles to premaxillary border 240 



Occiput to premaxillary border 265 



Breadth across post-orbital processes 86 



