130 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



Table 28. — Comparison of dentition of six genera of Mixodectidae 



A possibility worthy of serious consideration is that the Phigio- 

 menidae may be reLated to the Mixodectidae. They show the follow- 

 ing principal characters suggestive of such a relationship: 



Molarization of premolars somewhat similar to mixodectids (except Mixodectes 

 and Indrodon). 



Uppep molars with, feeble hypocone shelf and pronounced and peculiar median 

 transverse valley (as in Elpidophorus and to a less degree some other mixodectids) , 

 and otherwise generally but more vaguely similar. 



Tendency to emphasize external shelf of upper molars and to develop cuspules 

 on it (but see below). 



Elevation of internal over external cusps of lower molars (a tendency in all 

 mixodectids, pronounced in Elpidophorus) . 



Lines joining protoconid to metaconid and hypoconid to entoconid parallel and 

 anterointernal-posteroexternal (tendency in mixodectids, pronounced in Elpi- 

 dophorus). 



Paraconids, and trigonids generally, similar. 



Molar talonids markedly broadened. 



These, and a few minor details, produce a general type of dentition 

 common to plagiomenids and mixodectids and not, as far as I know, 

 to any other groups, ^^ 



" This was evidently partially noticed by Matthew (1918, p. 600), for he notes the resemblance to Ptagio- 

 mene of "an undescribed genus from the Paskapoo beds", which was undoubtedly Elpidophorus, not then 

 named and not until very recently known to be an aberrant mixodectid. 



