Mekriam.] 



Pliocene and Quaternary Canidae. 



285 



have been lost but were evidently quite small, as there is but 

 little space for them between I- and the median premaxillary 

 suture. I- is veiy large and in this respect resembles the 

 hyaenas and some of the Aelurodons. The canines are not large. 

 They tend rather to be smaller than is common in the Canidae. 

 P 1 , 1 & - have been lost but the alveoli show them to have 

 been closely crowded. They were evidently small, though P- and 

 P- were two-rooted. The carnassial is wide and heavy. The 

 protocone blade is situated rather far forward. The deuterocone 

 has disappeared, though the inner root is present. On M-, the 

 metacone is noticeably reduced, the heel and the whole inner 

 lobe are small and the tubercles very low. The anterior inner 

 angle is extended forward from the protocone forming a char- 

 acteristic shoulder. M- is very considerably reduced. 



Affinities. — The relation of this form to that represented by 

 the type of the genus Hyaenognathus is a particularly interesting 

 one. Each is represented by a single specimen and they are found 

 in beds not differing widely in age. Both represent short-muzzled, 

 broad-palated types of canids with dentitions which are specialized 

 but still not greatly reduced numerically. Unfortunately we 

 have no corresponding parts for comparison, so that the true 

 relationships between the two can not be determined with 

 absolute certainty. Some of the features of the dentition would 

 seem at first to show that they are very different. In the 

 superior deutition of Porthocyon, P-, which opposed the anterior 

 side of inferior Pt, is a small tooth not corresponding in size to 

 the large Pt of Hyaenognathus. Also, the greatest width across 

 the mandible of Hyaenognathus is across Pt, or some distance in 

 front of the carnassial, while in Porthocyon the width of the 

 palate is greatly decreased immediately in front of the carnassial. 

 On the other hand, we find that in the hyaena, in which some- 

 what similar structures occur, the large P3" standing at the point 

 of extreme flare of the mandible is opposite the point where 

 contraction of the palate begins and strikes either against or 

 outside the posterior portion of a small P-. In Porthocyon P- 

 is moved so far inward that it stands in front of the inner root 

 of the carnassial, and it may have had much the same relation to 

 Pt in occlusion that we find between P- and Ptj in the hyaena. 



